My cat has a small knot at bottom of his tail by his spine and acts like its very sore what can I do for him if in pain

A trip to the VET if they are in obvious pain.

Nothing, human medications are very dangerous and cats have sensitive systems.
You should ONLY give medications when prescribed or approved by your vet.
Are there other cats that may have bitten or scratched him?

If a cat is showing pain then you can bet that they are in excrutiating pain. It's in their nature not to show pain, especially to people, because it is an indication of a vulnerability. In the animal kingdom, vulnerable animals become targets and are usually killed.

The lump or knot you see could be many different things. Some of those conditions can be fatal. Please seek veterinary attention as soon as possible. In the meantime, keep your cat indoors, preferably in a quiet place - like a large cat carrier, dog cage or a small room in a quiet area of the house. Provide a soft bed, food and water. If there is enough room, include a litter box.

Please check your cat's inner bottom eyelid by gently rolling it down a bit. Then check the inside of their mouth and gums. If the inner eyelid or gums are very pale, then take your cat to an emergency clinic immediately as they could be in shock.

As LadySam said, tempting as it might be, don't medicate. Most human medications are not suitable for cats and even if it would work you would have to know the dosage. Especially do NOT give Tylenol.

Hope this helps. Please update us when you are able.

Hugs, Didi