What is the real-world mountain that was used for filming the cable car scene in Where Eagles Dare?
The movie's Wikipedia article gives a list of all the filming locations:
the castle – Hohenwerfen Castle, Werfen, Austria; filmed in January 1968,
cable car – Feuerkogel Seilbahn at Ebensee (Austria); filmed in January 1968,
airport scenes – Flugplatz Aigen im Ennstal (Austria); filmed in early 1968. The exact place of filming is the "Fiala-Fernbrugg" garrison, still used by HS Geschwader 2 and FlAR2/3rd Bat. of the Austrian army. The big rocky mountain in the background of the airfield is the Grimming mountains, about 40 km east from the "Hoher Dachstein", or about 80 km east and 10 km south from Werfen,
other scenes – MGM-British Studios, Borehamwood, England; filmed in spring 1968
And the Wikipedia article of that location in turn says, that it's indeed the mountain that's called Feuerkogel:
Since 1927 an aerial tramway built by the Bleichert engineering company runs up to the summit of the Feuerkogel mountain [...] Parts of the 1968 Where Eagles Dare film were shot in the Ebensee area.