When Science ceases to be useful as a method to discover and explain things.
But on a more specific note, that’s impossible to answer, because you would have to know what that finite set of “knowledge of everything” is, if it is indeed finite. Since we can’t know what the upper limit of “what is knowable” is, it’s impossible to even roughly project when we might know almost everything.
To complicate matters, you can’t even break the problem down. How about half of everything? A third of everything? One-tenth of everything? How much do we currently know compared to those subsets? We simply don’t know.
And what if we discover other dimensions? Or what about another universe? What if there’s infinite universes to discover? Knowledge is emergent as a result of doing science, so as long as there’s something we don’t know, we’ll have scientists out there doing science (or whatever its successor is).