From Longman Dictionary of Contemporary Englishbe well up in/on somethingbe well up in/on something (also be up on something American English) informal to know a lot about something I’m not all that well up in musical matters. Conrad’s really up on his geography, isn’t he? → up
Examples from the Corpus
be well up in/on something• By eight o'clock, when the first pair was due to tee off, the sun was well up in a clear sky.• But deep inside there was a brooding that was welling up in him.be well up in/on somethingbe well up in/on somethinginformal especially British EnglishKNOW something to know a lot about a particular subject Geoff’s always been well up on the internet. → wellExamples from the Corpus
be well up in/on something• By eight o'clock, when the first pair was due to tee off, the sun was well up in a clear sky.• But deep inside there was a brooding that was welling up in him. 