If necessary, you can stop a cloning operation with a KILL QUERY processlist_id statement.

On the recipient MySQL server instance, you can retrieve the processlist identifier (PID) for a cloning operation from the PID column of the clone_status table.

mysql> SELECT * FROM performance_schema.clone_status\G
*************************** 1. row ***************************
             ID: 1
            PID: 8
          STATE: In Progress
     BEGIN_TIME: 2019-07-15 11:58:36.767
       END_TIME: NULL
         SOURCE: LOCAL INSTANCE
    DESTINATION: /path/to/clone_dir/
       ERROR_NO: 0
  ERROR_MESSAGE:
    BINLOG_FILE:
BINLOG_POSITION: 0
  GTID_EXECUTED:

You can also retrieve the processlist identifier from the ID column of the INFORMATION_SCHEMA PROCESSLIST table, the Id column of SHOW PROCESSLIST output, or the PROCESSLIST_ID column of the Performance Schema threads table. These methods of obtaining the PID information can be used on the donor or recipient MySQL server instance.