A traditional stud finder will have issues on a wooden floor. You can purchase a stud finder that also has a "nail finder" - basically a metal detector to help you find where the flooring was nailed/screwed in. You may have better luck determining where the floor joists are.
For the squeaks, it would depend on the flooring type, and whether it's the floorboards themselves or the subflooring/joists that are causing the squeak. Ideally, you'd want to attack the problem from the bottom using shims or, depending, screws from the bottom that won't penetrate fully through the floorboard. If access from the bottom is unavailable, your choices become much more limited. If you have a tongue-in-groove type flooring, that makes it even more difficult. If using plank flooring with the ability to remove a board or two around the squeaking area, then that's not too bad as you can nail/screw in the subfloor and then reattach the planking securely.
I've heard that you can also use baby powder (sprinkled into cracks) to keep planks from rubbing against each other if this is the cause of the noise. You'd probably need to re-apply seasonally, though.