What visual artifacts are expected from the JWST? What visual artifacts should we expect from the images that will be released from the James Webb Space Telescope? Specifically, do we expect 3-pronged diffraction spikes (any preview how they would look?) and do we expect any artifacts due to the honeycomb-like structure of the main mirror?
Are you asking about the PSF (point-spread function)?

There are some simulations at http://www.stsci.edu/jwst/software/webbpsf ; there are some basic images available at that site as well as a downloadable package you can use to compute the PSF for a particular instrument and wavelength.  Since the telescope hasn't been fully assembled yet these are based on simulations.