RemoveMultiKnot should remove fully multiple knots from surfaces as well as curves.
Currently the only way I know to remove full multiknots from surfaces is tedious repetitive applications of the RemoveKnot command which has a high probability of inadvertently removing a multiknot, not completely removing a multiknot, or missing one or more multiknots.
A similar request was made in 2017 but implementing it appears to have stalled because it also included a request for an angle tolerance test. https://mcneel.myjetbrains.com/youtrack/issue/RH-40309 Please implement removal of fully multiple knots from surfaces without an angle tolerance test.
File with examples of each:
FullyMultipleKnots.3dm (2.8 MB)