I don't believe that Dumbledore knew that the Marauders were Animagi while they were at Hogwarts, as Remus recounts in his tale to Harry about the Marauders:
‘I sometimes felt guilty about betraying Dumbledore’s trust, of course ... he had admitted me to Hogwarts when no other Headmaster would have done so, and he had no idea I was breaking
the rules he had set down for my own and others’ safety. He never knew I had led three fellow students into becoming Animagi illegally.
Prisoner of Azkaban - page 260 - Bloomsbury - chapter 18, Moony, Wormtail, Padfoot, and Prongs
And he follows this up with his internal struggle to let Dumbledore know that Sirius was an Animagus.
‘All this year, I have been battling with myself, wondering whether I should tell Dumbledore that Sirius was an Animagus. But I didn’t do it. Why? Because I was too cowardly. It would have meant admitting that I’d betrayed his trust while I was at school, admitting that I’d led others along with me ... and Dumbledore’s trust has meant everything to me. He let me into Hogwarts as a boy, and he gave me a job, when I have been shunned all my adult life, unable to find paid work because of what I am. And so I convinced myself that Sirius was getting into the school using Dark Arts he learnt from Voldemort, that being an Animagus had nothing to do with it ...’ - Remus Lupin
Prisoner of Azkaban - page 261-262 - Bloomsbury - chapter 18, *Moony, Wormtail, Padfoot and Prongs
I don't believe Dumbledore knew. If he's omniscient and did know, he kept it on the down low.