An Etymological Dictionary of the German Language/forschen
forschen, vb., ‘to search, investigate,’ from MidHG. vorsken, OHG. forskôn (rarely Franc. forspôn, with assimilation), ‘to demand, ask’; a form peculiar to HG., unknown to the remaining dialects, and pointing to Goth. *faúrskôn, *faúrhskôn. The sk is a derivative like Lat. sc (comp. dreschen, wünschen, waschen). Goth. *faúrskôn would be the normal form for faúrhskôn, like Goth. waúrstw, ‘labour,’ for waúrhstw. The Teut. root forh is identical with the root of fragen, from the pre-Teut. root pṛk (see fragen). An sc derivative is also seen in Lat. poscere (for porscere), ‘to demand,’ as well as in the Sans. root pṛch, ‘to ask.’