1 is a spare stack and it's 3" abs
2 is the toilet also 3"
3 is a vent and
4 is a sink.
It's a pretty bad rough in. If 3 is in fact a vent why is it so far away from the wall?
If it's for a shower/tub why is it so close to the wall?
This is what your rough in should look like
3 must be a vent.
This is an example of what is going on
If you can pour water down one of the 2-inch pipes and see that it holds water at level, that would indicate it has a trap as in the pipe at the far left of the image. Traps it only ever be installed at floor drains or shower drains it sink drain will not have a trap under the floor.
Your 3-inch that's close to the wall may be repurposed as a shower drain provided it's vented.
In your image pipe number 3 could very well be intended as a shower drain, just in a very poor location.