As title says.

What?! You should check out this, https://github.com/lucko/LuckPerms/wiki/Developer-API

If that doesn't help you'll need to be more clear. An issue that says a thing that's this ambiguous is painfully difficult to decipher

Also some examples here:

https://github.com/LuckPerms/api-cookbook/blob/master/src/main/java/me/lucko/lpcookbook/commands/GetPrefixCommand.java
https://github.com/LuckPerms/api-cookbook/blob/master/src/main/java/me/lucko/lpcookbook/commands/GetOfflinePrefixCommand.java