i tried with GET /api2/json/cluster/tasks.
{'pid': 2063, 'type': 'qmigrate', 'id': '102', 'node': 'serv-xxx', 'user': 'xxx', 'saved': '0', 'upid': 'UPID:serv-xxx:0000080F:086514BD:5EC28AA7:qmigrate:102:xxx:', 'starttime': 1589807783}
And with GET /api2/json/nodes/{node}/tasks/{upid}/status...