After resistance, French joiner Claude learns new skills (8)
I believe the answer is:
retrains
'learns new skills' is the definition.
(I've seen this before)
'after resistance french joiner claude' is the wordplay.
'after' says to put letters next to each other.
'resistance' becomes 'r' (abbreviation).
'french joiner' becomes 'et' ('and' in French).
'claude' becomes 'rains' (actor Claude Rains).
'r' put next to 'et' is 'ret'.
'ret'+'rains'='RETRAINS'
(Other definitions for retrains that I've seen before include "Repeats a course of instruction" , "Learns new skills" .)