How many skills can the kittens learn

There are three main ways to get coal. The first two you'll get are the Coal Furnace and Deep Mining upgrades at the workshop. These will let you get small amounts of coal for each mine (0.003 per tick, 0.015 per second) and running smelter (base .005 per tick, .025 per second).

But, by far the best source of coal, is unlocking the Geology technology, and assigning Kittens to the Geologist job. Geologists are worth .015 coal per tick , equivalent to three smelters, or five mines. And kittens can improve at their jobs; a Master Geologist is earning about 0.026 coal per tick, which is over 0.1 coal per second each.

There are also quarries, which each give a +35% boost to mineral production, as well as another 0.015 coal per tick. They won't improve on their own the way Kittens improve their skills, but they still help a lot.

There are also several upgrades at the workshop related to coal which can help. Pyrolysis will increase coal gains by 20% from all sources. The Geodesy will increase Geologists' base coal per tick to 0.0225, making even a Dabbling Geologist worth four and a half Deep Mining mines. It also allows Geologists to produce a small amount of gold while they work.

The main section, above the census, is where you increase or decrease the number of kittens on a given job. You don't get fine-grained control over which kittens are doing which job, but you don't really need it; removing a kitten from a job using the [-] button always removes the kitten who is least skilled at it (of those working at that job right now), and adding a free kitten always adds the free kitten with the highest skill in it. As of 0.9.9.2, you can remove a specific kitten from their job when you unlock the Census, but assigning still always assigns the most-skilled kitten.

Note that your kittens can be skilled in more jobs than display, so you may not always be able to tell at a glance, but under most circumstances, your kittens shouldn't be changing jobs too often anyway.