As a family with over 480 energy, I have a few recommendations on increasing energy for players. Please don't be too ambitious and expect to gain all knowledge quickly and easily. This is not feasible, and it is something that I feel takes time, planning, and concerted effort. For example, knowledge gain from amity with NPC and some discovered items/locations does require energy investment to acquire, so if you are actively spending energy, then you may find yourself having to acquire newly discovered knowledge at a time when your energy reserve is replenished. 

Firstly, I recommend acquiring a Calpheon Noble Suit/Dress. This item grants +15% amity when equipped. You should always equip this, when trying for amity gains with NPC. 

Secondly, it is a common misconception that higher-grade knowledge (such as having S grade) is related to energy increases. This is not true. Having ANY GRADE knowledge is the only requirement for getting energy gains. Therefore, say for example that you are playing in an unfamiliar zone on the map and encounter a new animal. The approach is to repeatedly defeat that animal until you see the message indicating that you've gained knowledge on it - be it C, B, A, A+, or S. All that matters is that this knowledge appears in the corresponding section (for animals, it would be found in Ecology) as filled in with the name animal instead of filled in with question marks.

Higher grade knowledge does impact your overall knowledge score and family fame rating that leads to higher drop chances, but it does not actually increase energy.

If your true objective is a more rapid increase of total energy, then make it a point, initially, to get ANY knowledge for unfamiliar mobs. You can always come back later and grind it up to a higher knowledge level later.

Along this same vein, when going to cities, make it a point to chat with all NPC and look for items that you can interact with. For example, if one goes to Duvencrune in the Dreighan zone, then there are fruit and vegetable carts that you can interact with for knowledge. Keep in mind that "notable NPC" that you have not interacted with previously  will be shown on your mini-map displayed with "?", so it is advised to interact with them all. 

Thirdly, another easy tactic for gaining knowledge is to purchase one of all available trade items from every trade manager NPC that you encounter. While the trade item is in your inventory, find and use it. The item disappears from inventory and knowledge about that trade item is gained.

Fourth, easy knowledge can be gained from farming using "basic seeds" purchased from seed vendors. I recommend buying several of all of the seeds available from the seed vendor in Calpheon. Plant a few of each seed in whatever fence that you are using and harvest them, once fully grown. Repeat planting/tending /harvesting of the basic plants until the knowledge on the crop is acquired. Additionally, you will want to follow all of these steps but breed the plants instead of harvest them. This allows you to gain knowledge on the seeds (or hyphae for the mushrooms). 

Fifth, in addition to defeating animal mobs, gathering from them with a fluid collector, tanning knife, or butcher knife gives an additional chance to gain knowledge. Similarly, you gain knowledge on trees by chopping them with a lumbering axe, and you gain knowledge on foragable plants such as thickets and bushes by gathering from them by hand. 
Sixth, you should make use of as many alternate characters as you can have. I recommend leveling them to level 7 (for faster switching of characters without needing to fully disconnect and re-connect) and "parking" them in Velia near Alustin the alchemist. He has an exchange option called The Realization of Energy that allows you to exchange a character's energy into various sizes of consumable energy potions (that can be stored, transferred between characters, and sold on the Central Market). I have often personally exchanged  lots of my alternate characters' energy for energy potions and transferred them to my main character. I found this to be a big help with situations where I was using greetings for large amity gains with particular NPC such as Philaberto Falasi in Port Epheria (where he required 1000 amity). 

Finally, use:

https://bddatabase.net/us/knowledge/

On this site, you can see a full listing of the available knowledge and systematically get any missing ones. Keep in mind that there are many found from having a certain amity level with specific NPC throughout the world. I wish that I could say that the amity mini-game was less brutal, less annoying, and required less energy, but those'd be a bold-faced falsehoods, and it's bad to lie to new players.

Presuming that you aren't aware of what is meant by "the amity mini-game", it is found when interacting with NPC and selecting the Conversation option. This activity costs energy per conversation and can yield huge amity gains, when successful. I really don't want to get into the specifics of the amity mini-game mechanics outside of calling attention to its availability because, to be honest, I'm not convinced that I am any good at it and wish to avoid imparting bad advice. 
Regardless, as you can see in the top-left of the screen, when you first interact with an NPC, the current amity level is displayed followed by any quests, knowledge, or buffs said NPC can give when having an amity level above the required level listed. This makes amity a necessary evil in my opinion, especially for those of us after the highly coveted God of Knowledge character title. 

On the plus side, when you have higher energy reserves, you can use the Greet option to repetitiously wave at an NPC for small amity gains per greeting. This costs 3 energy per greeting and is a guaranteed way to raise amity by 3 points without any risk of investing energy using a Conversation option with the NPC and failing the mini-game. You can gain additional amity by greeting, if you also wear the recommended Calpheon Noble clothes, drink an Elixir of Amity, and eat Pickled Fish. This approach seriously works great. I personally recently raised an NPC at Lemoria Guard Post up to 601 amity by simply waving at them for 10 minutes, like an idiot.

In conclusion, I really hope that this guide helps you in some way. Like Lara in Heidel says, "Take a look around, adventurer. This place is full of pleasant surprises." I personally hope that you find all of those surprises and gain knowledge about them for easy energy.