Like pitch Jack’s seen near railway (5)
I believe the answer is:
tarry
'like pitch' is the definition.
(pitch is a mixture made from tar)
'jack's seen near railway' is the wordplay.
'jack' becomes 'tar' (both are informal terms for sailor).
'seen' means one lot of letters go next to another.
'near railway' becomes 'ry' (abbreviation. I am not sure about the 'near' bit.).
'tar'+'ry'='TARRY'
Can you help me to learn more?
(Other definitions for tarry that I've seen before include "Drag one's feet" , "Stay longer than intended" , "Leave very slowly" , "Dawdle" , "Like fresh road surface" .)