Bi-directional links are visible if you go to the What Links Here [0] section of a page. Notably though it doesn't include "unlinked references" (as Roam refers to it), which is quite useful.
You can still fish that up if you need to either from the UI's search or the search API, but in poking Roam that felt like a potential anti-feature around ambiguous terms, for instance with no clear way to flag a particular reference as not relevant to a term.