This is untested (for obvious reasona), but you could try:
var query = from app in db.wfapp
where db.wftrn.Where(x => x.approver_id==32060)
.Select(x => x.wfapp_id).Contains(app.recgid)
select app
Let me know whether it works, though.
Alternatively: consider writing it as SQL; most ORms offer a pass-thru mechanism.