On , I learnt ...
Asana has some magic search terms
If you use the “Search this project” widget (via the “…” link on the right-hand side of the project view), you can search for:
"nobody"
to see unassigned tickets"not me"
to see tickets assigned to anyone but you
Found via https://forum.asana.com/t/search-for-unassigned-tasks/4770
Quite basic functionality really but I almost gave up trying to find it.