see https://forum.inaturalist.org/t/is-there-an-easy-way-to-open-all-notifications/25913/35
i don’t think the tool works directly to answer this particular question, but it could used as one step of a multistep process to answer the question, or since:
… the tool could be used by the person you’re tagging as an alternative interface to help improve her workflow.
…
but you can also sort of answer your question by using other tools.
if you mentioned the other user in standalone comments (as opposed to in the notes of an identification) you can find those by searching for the user’s id in your comments: https://www.inaturalist.org/comments?mine=true&q=[other person’s user id].
if you mentioned the other user in the notes of identifications (as opposed to standalone comments), you have to go through all those identifications since i don’t think you can search within the identification notes, but you can filter for, say, a particular taxon or place or date range, to narrow things down. here’s a page that will help you see your identification notes in the rightmost column, and there’s also an indicator of the sequence of your identifications so that you can tell from a glance whether there was a successive identification added to the observation: https://jumear.github.io/stirfry/iNatAPIv1_identifications?user_id=margaret_eaglecap&per_page=200.
if you know how to code a bit, you could automate the process of searching through identifications (not comments) a little bit using the API, but i don’t know that the time it would take to code that would be less than the time it would take to just visually scan through the page noted above.