You can use an expandable plug. First though, you need to figure out what that pipe is. Why is it just open, and why is it wet? If it's just a pipe sticking out of the ground there shouldn't be water in it. If it's a floor drain, it should be trapped; in which case you would see standing water in it all the time. Also if it's a floor drain it's there for a reason and can't be capped. If water is backing up out of it, then you have a blockage somewhere.So I am in my new house and I find a damp area in my basement that looks moldy and decide it has to come out, after wrestling with the framing the damp seemed to get worse. There was a steel filing cabinet built into the framing I decided to move that out as well so it could dry. After I moved the filing cabinet I found the source of the damp. "Someone" had cut what looks like a cast iron pipe that appeared to be a 2" drain almost flush with the floor, then put the filing cabinet on top but failed to cap the pipe in any manor. I don't know the best way to cap this pipe, I have seen 2" rubber Fernco caps that look like it would work but I wonder if there is a better solution?
Can you post a picture?