From the game's encyclopedia
An Interaction used by Ecclesiastical Rulers to expand their Clerical Region into the De Jure Counties of an adjacent Duchy.
This is only possible with the approval of the Head of Faith.
The game's text for patch 1.20.1.2. Words in blue are entries of the encyclopedia: hover one to read it, as in the game.
Request Clerical Title Expansion is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "An Interaction used by Ecclesiastical Rulers to expand their Clerical Region into the De Jure Counties of an adjacent Duchy." Patch 1.20.1.2, from game/common/game_concepts/pam_game_concepts.txt and game/localization/english/game_concepts_l_english.yml.
Source: game/common/game_concepts/pam_game_concepts.txt, game/localization/english/game_concepts_l_english.yml and the English localisation, Crusader Kings III 1.20.1.2.