。
I'm fully aware of it.
Literal
Ten-thousand-ten-thousand understanding's above [copula-です].
A formal, emphatic idiom. 万万承知 uses 万万 as a doubling intensifier ('absolutely,' 'completely,' 'ten-thousand-fold') attached to 承知 ('acknowledgement, consent'). の上です adds the 'on top of having done that' sense — 'I understand it fully and am acting with that understanding.' A stiffer, formal register, often used to assert resolve despite warnings.