Sight of German — is one inside? (6)
I believe the answer is:
vision
'sight' is the definition.
(I know that sight can be written as vision)
'german is one inside?' is the wordplay.
'german' becomes 'von' (common element in German surnames).
'one' becomes 'I' (Roman numeral).
'inside?' means one lot of letters goes inside another.
'is'+'i'='isi'
'von' enclosing 'isi' is 'VISION'.
'of' acts as a link.
(Other definitions for vision that I've seen before include "Sight of unusual beauty" , "Imagination" , "Dream" , "Sight or insight" , "The power of seeing" .)