What's the challenge exactly? Looks like nothing troublesome to model. Make a profile and extrude or combine a few primitives or sculpt from a sphere . There could be gazillion ways.
looks like a scan, but... whatever techniques you use to model other things will also work with this. What sort of modeling have you done already? Why don't you think it would work here?
yeah looking at the lowpoly, how straight the lines appear. i assume they built the lowpoly first, then used it to create the highpoly, not sure if it was actually sculpted or maybe just smoothed, baked and all surface detail is just done in a software like substance painter.