The ISS has an X-ray telescope called NICER and this answer in Astronomy SE (and links therein) explain that it was able to show that there are hot spots clustered near one pole of the pulsar PSR J0030+0451.
There have been several mentions of a telescope inside the ISS that people can point out a window, but I don't think this can be used practically for astronomical observations.
Skylab had an ultraviolet telescope which produced a great deal of new observations at wavelengths only observable from space. How did Skylab's electrographic ultraviolet camera work?
Besides NICER at X-ray, at what electromagnetic wavelengths have astronomical observations been made from the ISS, and what kinds of particles besides photons have been imaged or directionally resolved?