From Longman Dictionary of Contemporary Englishbe knocking on the doorbe knocking on the doorto be wanting to join a group or team – used in news reports Five countries have permanent seats on the UN Security Council, but Germany and Japan, among others, are knocking on the door. → knock
Examples from the Corpus
be knocking on the door• But a kiss denied, for Phillis was knocking on the door.• Soon Pugwash was knocking on the door. 