How do I determine that a particular TP (or SL) closes a position completely, not partially??

In the system of copy trading, orders from the master trader’s account arrive from websocket. How do I know that this order close position for all quantity. When a position is closed via TP or SL, the parameter Reduce is True. Are there any other parameters that can be used to determine whether a position is completely closed or not?

There’s no way to know directly, you need to keep track of the position’s quantity locally by checking the executed quantity from websocket events.