(Java Minecraft 1.14) How to use /data with an nbt path?

Solution 1:

"Child" tags are just tags inside other tags. Like "memories" is a child tag of "Brain".

The string notation is a bit misleading, you can't actually use it for strings in NBT. It's used if an NBT tag's name contains special characters, like a period, a square bracket, etc. No normal Vanilla NBT tag contains such special characters, but it is possible in a few places to use custom NBT tags.

If you want to get the damage on the item in your hand, use /data get entity @s SelectedItem.tag.Damage 1. The Player.dat wiki page shows player tags, and if you use SelectedItem (which returns an item) you need to look at the Item Structure tags, and see that the tag: tag has information about the item itself. Going to the general tags shows you the Damage tag. Therefore, you chain these together to get SelectedItem.tag.Damage.