Often, they do not install a trap...you'd want to verify whether one is there or not. If there is one, you'd pour some water down it, then look to see if you can see any standing water that should be held by the trap, if it is there. Then, you need to determine if the pipe is really 1.5" (which is okay for a tub), or 2" (which is required for a shower). In some places, they require at least 2" pipe below a slab.
If you want the whole room to be handicap accessable, with a barrier free shower, then you either need to recess the shower area, or build up the floor with to allow for proper drainage. It's nicer to recess the thing, then there's no ramp coming into the room. An accessable shower begs for a linear drain, but your stubout is in the wrong position for that (might be easy to move). With a linear drain, you can slope the entire floor, so no need for multiple pitches.