The method for locating pinhole cameras is the same as the method for locating field spiders. All you need is a source of light like a flashlight and decent eyesight. It also helpful to have a toilet paper tube.
Step 1: Get a Tube
Find a tube that's good for looking through. A cardboard tube from a roll of toilet paper or paper towels is best.
Step 2: Get a Flashlight
All you need is a flashlight or something that you can use to focus a beam of light in a dark room. Attaching a couple of directional LEDs to the outside of the cardboard tube can work also if you don't have a flashlight.
Step 3: Look Through It.
With one hand, hold up the toilet paper tube to your eye. With your other hand, hold up the flashlight at about eye level and point it away from you. With one eye, look through the tube and scan the room. If there are any small points of light bouncing back, inspect it further. It might be a camera.
Step 4: I Found One.
If you found a camera, it can be easily disabled simply by putting something in front of it. If it is in the wall, hang a poster over it. If it is in something like a flower pot, put a box in front of it.
Or you could just unplug it, but that would make it very clear that you know they're spying on you.