plumbing rough in

I have a house that was built in 2004, I am in the process of getting ready to build a bathroom in the basement. The basement has a concrete floor and it also has roughed in plumbing. There are two pvc pipes sticking up through the concrete, one is a 4" pipe for the stool, fourteen inches behind that, center to center, is a two inch line for the sink drain, this is not directly behind the 4" line but off to the side a bit, in the subfloor above is a pvc stub intended for a vent line, this line runs up into the attic and connects to the main vent line. The concrete wall is located four feet from the center of the 4" line. In between the 4" line and the wall is a pit with a two inch line which is blocked off. It seems to me that when I stud in the wall, which will lessen the 4 foot line by about five or six inches there will hardly be enough room for the shower, and sufficient clearance between the shower and the stool. I am in the process of breaking up the floor so I can redirect the two inch line in the pit the other direction which will put the shower completely clear of the stool. My plan is to cut the two inch line back, a distance yet to be determined, install a 45 degree elbow in the opposite direction as the present, and then run that line to the drain of my new shower. My main question is this. The two inch line in the pit goes under the concrete floor and I am wondering if there is a trap in that line before it gets to the main sewer line, or, do I need to put a trap directly under the shower drain? I have uploaded a picture for clarification.

The 2" was most likely planned to be in the wall and serve as the lav drain and wet vent for the rest of the fixtures.

I kind of figured the same with the 2" line and do plan on putting it in the wall. The line in the pit is for a bathtub, but I plan on putting in a shower instead which means I have to move the line. I don't think that after I stud in the wall that there will be much room between the shower and stool so do plan to cut the existing line back and install another 45 degree elbow in the opposite direction which will enable me to move the shower further down toward the buckets. I can then build a second wall about 30 inches (rough guess for now) wide from my stud wall and this would allow me to put a toilet paper holder to the side of the stool, then turn the wall back toward the studded wall and this would then become the front wall of the shower with the drain maybe one foot back from the wall and under the shower head. My question is still, would the line in the pit have a trap back further under the concrete before it connects to the main sewer line, or do I need to install a trap at the drain of the shower?

A "good" plumber would NOT have installed a trap in the line, other than at the end inside the "pit". But, then a good plumber would NOT have put an elbow there either, so it is impossible to say what you have there.

FWIW, regarding the toilet, code requires 15" either side of centerline to any obstruction, and 12" from the FINISHED wall is the most common rough-in. Depending on what you use for a wall, that 14" could be an issue from the wall, and that 30" of space centered on the toilet may be an issue to other things in the room.

You need a trap below your shower, not somewhere off to the side some distance away, otherwise, hair, soap scum, and other crud will build up and smell. The trap, when directly underneath the drain, means there's much less surface area to accumulate stuff like that.

That makes sense about the trap, I will put one in under the shower. I currently have two lines from my water softener going into that two inch line.I don't think the toilet will be an issue. I plan to move the shower down toward the buckets which will enable me to leave plenty of room between the finished wall and the toilet, as for the other side of the toilet, there will be a pedestal style sink and I can really make the bathroom as large as I want so there should be no issue with the toilet other than the vent for the toilet is a bit close but I can deal with that to maintain the proper clearance. One other question, I will move the drain for the shower toward the buckets, place the trap under the shower drain, now, does this need to also be vented? If so, can I just vent it right into the vent for the toilet, as this line will also serve as the drain for the sink?