City company finally invested in Geordie undertaking (3,4)
I believe the answer is:
new york
'city' is the definition.
(New York City is an example)
'company finally invested in geordie undertaking' is the wordplay.
'finally' suggests the final letters.
'invested in' means one lot of letters goes inside another.
'geordie' becomes 'NE' (Geordies are from Tyneside in the North East).
'undertaking' becomes 'work' (I can't explain this - if you can you should give a lot more credence to this answer).
The final letter of 'company' is 'y'.
'ne'+'work'='nework'
'y' going into 'nework' is 'NEW YORK'.
Can you help me to learn more?
(Other definitions for new york that I've seen before include "American state" , "City known as The Big Apple" , "major city" , "Queens here" , "City ''so good they named it twice''" .)