Knowledge is how much you know about each profession in the game. You gain knowledge simply by playing the game. For example, Horticulture knowledge makes it so you can grow herbs at KaldaBerth Gardens. By default, you can only grow Green Herbs. Once you have 11 knowledge you will be able to grow Red Herbs and by increasing your horticulture knowledge further you will be able to grow more and more potent herbs and grow larger amounts of each. This is how most areas of knowledge work, the more knowledge points you have in that section, the more of it unlock.
Please note: You lose 1% of a randomly-chosen area of knowledge at each reset.
Below are the descriptions for each area of knowledge to you (with job names in brackets):
Chemistry (Chemist) With enough knowledge in Chemistry you can create Synthetics at Chem Chemical for use in the Clearing.
Fishery (Fisherman/Fisherwoman) Improved marine harvests and greater stamina at The Docks are a direct result of Fishery knowledge.
Gambling (Card Shark) Make money the honest, hard way, gambling away your days at Georgetown's lovely casino. The more knowledge of Gambling you have, the higher your betting cap at Georgetown's Casino.
Horticulture (Healer) Knowledge of Horticulture enables you to grow and pick more powerful herbs in Georgetown's Kaldaberth Gardens, and as your knowledge increases you may get a higher yield from your herb crop.
Leadership (Drill Sergeant) Knowledge of Leadership enables you to train troops at the Training Center for use in the Clearing.
Meat Curing (Meat Curer) Knowledge of Meat Curing enables you to produce food for Clearing troops at the Smokehouse.
Mining (Miner) Knowledge of improved rappelling and cavern descending techniques allow for great and deeper access into the depths of Sol's Pit, and increases your ability to avoid the usual obstacles that exist in sub-terrain exploration..
Quantum Wokking (Chinese "Chef") Knowledge of Quantum Wokking, combined with knowledge of leet, lets you cook up Syn at Lee Hwon Fook's Chinese restaurant in Georgetown.
Religion (Priest/Priestess) Knowledge of religion allows you to join two souls in holy matrimony at the Wedding Chapel.
Rocket Science (Actually I am one) Knowledge in Rocket Science lets you produce spaceship components a Maxxon Aerospace.
Smithing (Smithy) Your knowledge of smithing can be put to good use creating weapons and armor at G'Town Fabrication.
Spacefaring (Captain) Spacefaring is your knowledge of the vast space around Sol Prime.
Tech (Master Builder) Use your knowledge of tech to create constructs in the Workshop for use in the Clearing.
Thieving (Pickpocket) In the heat of battle quietly slip your hand into your opponent's pocket, grab whatever you can find. Hopefully it'll be credits. The higher your level of knowledge in thieving, the more you can steal.
Warfare (General) Warfare knowledge gives you the ability to earn daily combat moves in the Clearing.