How to apply shortcut to "Show whole scene transparent" ? How to apply shortcut for selecting invisible backside parts of mesh? 
It called "Limit Selection to Visible" option in 2.7

There was an answer for 2.7:
Assign a shortcut to &quot;Limit selection to visible&quot; toggle
It doesnt work in 2.8
Was looking for the same and just found it.

In Blender 2.8 it is called Toggle X-Ray and the default shortcut is Alt+Z.