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This question asks whether any ground-based telescopes can see the James Webb. The answer ("yes, but it's basically just an indistinct dot") is deeply underwhelming. If only we had a much better telescope that we could use to look at it...
What would the James Webb see if it imaged itself from Earth Orbit?
The answer is going to be deeply underwhelming regardless of what telescope you use, because of the sunshield, and because of its location.
It lives at the Earth-Sun L2 point, as shown on this handy diagram from wikipedia:
this means we will always be on the sunward-side of the device, which means all we will ever be able to see is the sun-side of the sun-shield. Wikipedia has this image:
That's a visible-light rendering, of course, and I'm not entirely sure what it would look like in the IR spectra that the JWST sees in. NIRCam can see 600nm light (orangey). I can't see what angular resolution it has for visible-light imaging, but for near IR at 2000nm it is 0.07 seconds of arc. The face of the sunshield will be at a nice warm 383K so it'll be visible to at least one of the JWST's sensors, I'm sure.
The L2 point is ~1.5 million km away from Earth, and at that distance 0.07 arc seconds is equivalent to a feature size of a little over 500m. Given that the JWST is 20m long in its largest dimension, you're not actually going to get a blurry image... you're going to get a single pixel. Technically, it might be quite sharp. Just not very interesting.
