Do all stars have atmospheres?
Yes they do. Although a stellar atmosphere differs from a planetary atmosphere. It is very small if we compare it to the star.
*If you meant corona or the outermost part of the stellar atmosphere/ or just the outer atmosphere: No
While all stars on the main sequence feature transition regions and coronae, not all evolved stars do so
We think, that only some giants, and just few supergiants, possesse coronae.