Beautiful, took me a hot minute to find it because I'm on mac. For anyone else struggling with this, the path was
Macintosh HD/Users/"Username"/.gradle/caches/forge_gradle/minecraft_repo/versions/1.16.3/client-extras.jar
For clarification, I'm modding minecraft version 1.16.3, this path may change a bit in the future depending on future forge updates. Follow whatever path is necessary. The .gradle folder is a hidden folder, press command + shift + dot, all at the same time to show hidden files. Lastly, the client-extras.jar is unable to be opened by the archive utility. I copied it to my desktop, erased the .jar extension and added the .zip extension instead, then I unzipped it with the archive utility. The loot table information I was looking for was in the unzipped file at
client-extras/data/minecraft/loot_tables/blocks
To create your custom vanilla loot tables, please refer to the answer at https://forums.minecraftforge.net/topic/74709-1144-replace-vanilla-loot-table/
Happy modding.