How do I remove a bathtub handle with no visible screw?

See the little seam on the handle? You should be able to take a flat head screw driver and gently pry the two sides apart. The screw should be in there.

look underneath the sink. handle might have a "bolt" holding in place ,

find name of company and call customer service

look at a big box store for same fixture and see if it give details

Go underneath the sink and with a flashlight check it out. Screw or bolt is probably on backside.

Is it the faucet (centre piece where the water flows out of) that is leaking, or one of the handles that control the hot or cold water?

On the side of the faucet that is facing the camera, there is a little hole. It could be that the fixture is held tight with a hex bolt. To loosen it, a hex key with a hexagon end is required. These come in stainless steel, black or silver, in different lengths and sizes. Examples are shown below.

I can't say for sure from only one picture if this is how your particular brand of faucet set is tightened, however, I do know that it is a common attachment for heavier weight wall hooks in public restrooms or hotel bathrooms.

You have to get in cabinet underneath faucet and loosen a ring tightened around the handle

You have to loosen the hex screw that is located by a small hole under the lever, then replace the cartriage or washer to stop the leak

You can see the small hole in the handel. Use an Allen wrench to loosen the set screw. Be sure to use cut off valve under sink to cut water off before starting project. An assortment of Allen wrenches are not expensive and should be in every house hold tool kit.

You might have to unscrew the whole faucet.

My moen faucet just unscrews at the base under the handle. You just turn the base to screw and unscrew it and the whole handle and base assembly lifts off. The handle itself doesn’t come off the assembly.

Thanks everyone! We will try out everyone’s ideas this afternoon

Do you know the brand? Every brand has a web site.