Knob, lump (4)
I believe the answer is:
node
I believe this clue is a double definition.
'knob' is the first definition.
(I know that knob can be written as node)
'lump' is the second definition.
(I've seen this in another clue)
(Other definitions for node that I've seen before include "Where network lines meet" , "Where conductors meet" , "Intersection in a network" , "Done to a small lump" , "Point of intersection" .)