The base information for the warning message is contained in the node log file for the Lookup node. The node log files are stored in a sub-directory of the Analyze instance's site directory at:
site/data/executions/<username>/<dataflow name>/<run uid>
The folder will contain the intermediate data for the nodes in the data flow execution and the corresponding log file for each node.
The log file only identifies the first occurrence where a duplicate key use was detected.
The error message indicates (for the first occurrence only) the record number on the 'lookup' input that contains the first instance of the the duplicate key and the corresponding record number on the 'lookup' input containing the duplicate key.
The log also details the metadata for the 'data' and 'lookup input pins, and the output metadata.
Note. if there are multiple key values that have duplicates on the lookup pin these other duplicate occurrences are not logged.