Hey,
What is the permission node for the custom commands i made?

For example ''/mine'', how do i make a spesific rank (PEX) get the permission to do /mine?

You'd have to refer to the documentation of MyCommand

In examples.yml the setting is like this:

MineA:
command: /mine
type: ALIAS
alias: /warp a
permission-required: true

What would the permission node for this be?

Plugin: https://www.spigotmc.org/resources/mycommand.22272/

It also says:
You can use a custom permission for commands,by putting the permission-node line in the interested command.Or if you want disable the permission check for an single command you can use the "permission-required" command field.

Not sure what they mean with that.

Yeah, I don't know what it is.

You can use this to work it out: https://github.com/lucko/LuckPerms/wiki/Verbose