Its from the fantastic LFCHistory site.
https://www.lfchistory.net
https://www.lfchistory.net/About
This list includes assists from post-war seasons from 1945/46 onwards. Note that all assists haven't been resolved as reports do not include all potential assists and are dependent on LFChistory.net's interpretation of the phrasing of the reporters at those games before assists started to be officially counted. Our research has been very thorough comparing different sources to determine if an assist should be given. We feel that more than enough issues have been resolved to give a real sense of who are the assist kings of Liverpool FC.
An assist is credited to the goalscorer's teammate who touched it last before the goalscorer whether it was deliberate or not. No assist is given a) if the ball is deflected of an opposition player including keeper to goalscorer, b) ball is saved by keeper or blocked by an opposition player to goalscorer, c) ball rebounds off post/crossbar to goalscorer.
https://www.lfchistory.net/Stats/PlayersAssists