Find old moggy in middle of glen (6)
I believe the answer is:
locate
'find' is the definition.
(locating is a kind of finding)
'old moggy in middle of glen' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'moggy' becomes 'cat' (I've seen this before).
'in' indicates putting letters inside.
'middle of' indicates the central letters.
The middle of 'glen' is 'le'.
'o'+'cat'='ocat'
'ocat' inserted within 'le' is 'LOCATE'.
(Other definitions for locate that I've seen before include "Pinpoint, find" , "site" , "Discover place where thing is" , "Find, or establish in particular place" , "Lay one's hands on (something)" .)