How to Find Boc the Seamster and Complete his Quest

First Meeting - Northwest of Murkwater Bridge: Head northwest of the Murkwater Bridge Site of Grace. Look for a distinct tree, roll into it to reveal Boc. Speak to him and receive 10 Mushrooms. He will then mention going to a cave.

Second Meeting - Coastal Cave: Travel southwest of the Church of Elleh to find the Coastal Cave. Near the entrance Site of Grace, you'll find Boc. Enter the cave and defeat the two Demi-Human Chiefs to obtain the Sewing Needle and Tailoring Tools. Return to Boc at the cave entrance and give him the items. Speak to him until he has nothing new to say.

Third Meeting - Liurnia of the Lakes: After defeating Godrick and entering Liurnia, visit the Lake-Facing Cliffs Site of Grace. After speaking with Hyetta and refreshing the area, Boc may appear. Later, you can find him at the East Raya Lucaria Gate Site of Grace and the Altus Highway Junction Site of Grace, though he will have nothing new to say at these locations.

Fourth Meeting - East Capital Rampart: Reach the East Capital Rampart Site of Grace in Leyndell Royal Capital. Speak with Boc and ask him "Did you see it?". You will need to retrieve the Gold Sewing Needle from the Church of Vows in Liurnia of the Lakes. Return to Roundtable Hold and purchase a piece of Legendary Armor from Enia. Bring the Gold Sewing Needle back to Boc. You can then ask him "I'm sorry..." and he will remark on your armor. Hand over the Gold Sewing Needle.

Final Meeting - East Capital Rampart (Good Ending): Before progressing beyond the Mountaintops of the Giants, find the Prattling Pate "You're Beautiful" item in Hermit Village in Mt. Gelmir. Return to Boc at the East Capital Rampart Site of Grace, use the item in front of him, and speak to him. Reply "Yes" when he asks if you think he's beautiful.

Final Meeting - East Capital Rampart (Bad Ending): Alternatively, obtain a Larval Tear (purchased from merchants in Siofra River). Return to Boc at the East Capital Rampart Site of Grace and give him the Larval Tear. Exhaust his dialogue options. You will later find Boc transformed into a human near Rennala at the Raya Lucaria Grand Library Site of Grace.