An Etymological Dictionary of the German Language/Annotated/forschen
forschen, verb, ‘to search, investigate,’ from Middle High German vorsken, Old High German forskôn (rarely Franconian forspôn, with assimilation), ‘to demand, ask’; a form peculiar to High German, unknown to the remaining dialects, and pointing to Gothic *faúrskôn, *faúrhskôn. The sk is a derivative like Latin sc (compare dreschen, wünschen, waschen). Gothic *faúrskôn would be the normal form for faúrhskôn, like Gothic waúrstw, ‘labour,’ for waúrhstw. The Teutonic root forh is identical with the root of fragen, from the pre-Teutonic root pṛk (see fragen). An sc derivative is also seen in Latin poscere (for porscere), ‘to demand,’ as well as in the Sanscrit root pṛch, ‘to ask.’