The Protocol ability is defined as a character in the LEGO Star Wars games who is a protocol droid and can use protocol panels and activate whatever the panel activates.
In the games up to LEGO Star Wars III: The Clone Wars, protocol droids could interact with panels with C-3PO's face on them. In LEGO Star Wars: The Force Awakens, protocol panels were changed to be yellow panels where the player has to play a minigame to speak a different language. Protocol droids can also translate quest-giving NPCs.
In LEGO Star Wars: The Skywalker Saga, they can interact with yellow panels to activate certain things. Sometimes, these panels require passwords which the player will have to find in the area or on another planet. Protocol droids can translate all languages that NPCs speak.