My child flushed a flashlight down the toilet, how do I get it out?
The first (and most likely) place it's stuck is at the top bend inside the toilet. That's usually a rather tight turn. The second place is at the bottom, either above or below the floor flange. The bend going into the house drain stack is usually fairly gentle but there are ridges that can catch larger objects.

In short, there is no simple way to answer "where". The low-cost route is go and buy a wax ring, then pull the tank and bowl. you can then look up the toilet's internal trap and see if it's wedged in there, and stand a reasonable chance of getting it out with a wire.

If the flashlight is not in the toilet you will need to call a plumber. Get one with a fiberscope, not just a power auger - this isn't a blockage you can chop up and send down the pipe, you need to find it and extract it. We are not concerned about getting the light back, we are concerned it doesn't get stuck somewhere more expensive, like under the back lawn.