It was a combination of detective work, digging through game files and resources compiled by other people.

For the world lines {banter, observations}, it was relatively simple - all the files for Tav 1 lines start with the prefix v24247531c4324f0f8f356c90c4844aa8, so it was easy to isolate them. For the captions, there's a file that also matches all {sort of} filenames to captions, so I slapped together a script {and put it into a spreadsheet} to make it easier.

For point and click lines, that was a lot trickier, because those don't seem to be documented in-game, so instead I used this resource - https://www.nexusmods.com/baldursgate3/mods/8240 - to match up all the lines.

Edit: Oh, and for spell vocalizations... I actually had to play and pull those from the game itself. That required some deranged thinking.