I believe this is a holder/support for your electric/lp lines in the slide. On mine the lines and cords are attached to this so when the slide goes in and out it keeps them neat and keeps them from getting kinked.
I had that happen to my replacement part while my 5'r has been sitting still in an RV part for the past 9 months. Brand new part, still broke after one trip from San Diego to Arizona. I will be installing a quality metal hinge to repair the break.
2012 Ram 3500 DRW Crew Cab, 6.7 HO Cummins
2014 Columbus M-340RK
'69 Chevy C-10, 396BB
One end will be on a metal tube about a half inch in diameter. The other end is screwed to probably a piece of angle iron with two screws. Crawl under and look. It will be very plain where it is mounted. BTY, simply taking the broken piece off and screwing the remaining back will get you by until you can order a replacement.