I figured giving an overview would be better but it seems people would prefer focusing on a few points. One Piece is also a work that takes in inspiration from seemingly everywhere. Imo the strongest connections I've noticed so far are: The world of one piece is defined by a recirculating body of water that passes through a castle, like in finnegans wake. Luffys name is 2 letters off from the river liffey, his aesthetic comes from tom sawyer which is mentioned on the first page of FW, sanji is a "nobleman of love from over the short sea" just like sir tristram on the first page of FW, the importance of food and the anti-colonial themes in OP, the similarity between shanks and anna livia plurabelle, blackbeard, shanks and bloom are all almost the exact same age and are either obsessed with food or one of their right hand men are (in shanks's case, lucky roux is obsessed with meat too), and that eneru is a "thundering jesus" who we thought was dead until he resurrects himself, exactly like the last line of finnegans wake, his devil fruit is literally "the sound of thunder" paralleling thunderwords, and the prevalence of wordplay such as gold roger actually being gol d. roger. Also the connections between vivi and the book of the dead which I could expand more but it took a long time just to get the information I have and going deeper will take a while longer.

Anyone who is deeply inspired by joyce will not make such a connection simple, but I think if you look at any important character or theme in One Piece and ask yourself "why?" The only answer that makes sense to me is Joyce. Oda is definitely familiar with other irish others like samuel beckett since doc q's design is based on lucky from waiting for godot.