This fell off my truck today when I was washing it.
What is it and where does it go?

 

It's the oil catch thing it's not important at all

 

Where does it reattach?
If it is supposed to be on my truck, it is important to me.

 

It straddles the frame section under the oil filter. It guides the oil when you remove the filter to the drain points

 

It's called a "revision", it's an add-on to solve a problem that a d&*&^$$ engineer created, like placing the oil filter so that when you remove it the oil drains on everything possible on it's way to the drain pan.
We have similar items in the aviation electronics industry, primarily caused by cost cutting that trickles down to engineering just like in the auto industry.

 

It's held on by 2 screws-It's the piece marked 6N634

 

You mad huh?