There have been atomic explosions set off in space, filmed from the ground.

There have been atomic explosions detected from space, using specialized instruments.

But I don't think there has ever been a case where an atomic explosion was filmed from, say, a real-time space satellite. Part of this is that the technology of putting motion picture technology in space mostly post-dates the era of atmospheric nuclear testing.

The closest that I know of anyone coming to taking a picture of an atmospheric test from space is this pair of photos from 1964, of China, taken with a US KH-4 satellite: October 8, 1964 (8 days before the test); October 20, 1964 (4 days after the test).

It is not impossible that better footage of an atmospheric test has been taken by a satellite, but if it has been, it has not been declassified and released by the countries that would be capable of doing such a thing. The last Chinese atmospheric test, on 16 October 1980, would be a possible candidate, as the technology for photographing such a thing would have been pretty mature at that point. However that is near-enough in time that information on that is probably hard to get ahold of.

It would be a fun exercise (perhaps) to compile a list of all people in space at all times, and then compare that to atmospheric nuclear tests, to see if there were ever instances where someone in space, by looking out the window, could have possibly seen one. I don't have this data in front of me, though.