This doesn't seem to be possible today. I can't find any API on Lemmy/PieFed that supports tagging/notes. If they do support it it is currently not exposed to 3rd party clients.
Summit
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Oh I was thinking of user tags. Will have to figure out where to surface this information. Added to roadmap.
Sorry for the confusion. Im not sure if users actually use the local only "user tags" in summit, for me at least it would be best to just replace those with the notes that are synced with the servers.
Im actually not sure what "user tags" are on lemmy or piefed only saw that term used in summit.
EDIT: Thank you for putting it up on the roadmap :)
I don't think notes support the same functionality as user tags in Summit. In addition, their name suggests longer form text which means it likely shouldn't be surfaced in compact UIs such as a comments section.
The general feeling I get is that these two features seem to aim to solve the same problem but in slightly different ways.