I found the below link (another question) - this does not seem to be a correct answer and am urgently looking for a solution for the same.
After loading the ContentLoad - we can ContentNote.id from the successfile and yes we load ContentDocumentId field of the new csv file with headers ContentDocumentId, LinkedEntityId, ShareType, and Visibility
Later if we have to pick id field from Lead and map to the above csv file - how would we? we are not sure of linking the ContentNote.Id to the Lead.id.
So, i don't think this is correct solution. what do you say ? Did i not understand correctly ?