Great trails there...but...
..as the JTTC site says, some of them (the best ones unfortunately) are off limits. Of the legal ones, I'd try Twin Peaks and the Nesquahoning Rim Trail.
That said, I understand the network is not policed, either...but ride at your own risk. When it was open, we always had a blast on:
a) American Standard (Start at 6 and go to end of 7 on the "Broad Mountain Trail Network" link). that's about 12-15 miles
b) There's also Deer Path 1 and 2 to Pine Tar to the outlooks along Broad Mountain (1 to 2 to 3 and then back to 1 toward Glen Onoko on the same map). That's another 12-15
c) If you can manage the Uranium Road section too (#4) that's fun as well.
American Std is the most fun, largely singletrack, with stream crossings, rock gardens, swoopy and twisty descents.