That's the coolant inlet line to the EGR cooler.
Remove the hold down, that tube end seals with an O-ring....and when it comes out, I can guarantee you'll need a new one....I matched one up at the parts store, nothing special.
If you remove the EGR manifold for access, No new gaskets needed.
But if you remove the air box intake tube, some long reach needle nose pliers should do the trick without removing the tube.
2007 LBZ 3500 LT3 DRW Crew Cab, Sulastics, Putnam XDR 15K, B&W 30K-Turnover GN+Companion, Ride-Rite Air...EFI'd by Rob
2008 LMM 3500WT DRW Crew Cab, 8 'Flat/GN, Workforce Alum Toolbox, Ride-Rite Air Use-ta Haves 2006-6.0 3500 WT DRW ExCab Flatbed, 2005-LLY 3500 LS DRW Crew Cab, 2002-LB7 3500 LS DRW Crew Cab I Live my life in such a way that when my feet hit the floor in the morning...Satan shudders & says "Oh shit, he's awake!"