'Last knockings' originally meant last wages/earnings. Thus, to 'be on the last knockings' meant to approach the end of a period of employment.
Since then, it has come to be applied in other circustances such as the tail end of a pub session...before 24-hour opening, of course! So, if someone came in at 10.50 pm in the old days, people might say he'd arrived 'at the last knockings'.
'Last knockings' appears to have nothing to do with games, though 'last knock' often does, as in one tennis-player saying to another towards the end of the evening, "Let's have a last knock before the light goes."