Pinning convention for Panasonic P5KS connectors AXK5S24047YG and AXK6S24447YG
The 'First' pin is not really a standardised thing for connectors like this. In my experience this would come down to your workplace’s general design conventions.
For example, my workplace would pick based on the top down view of the PCB side Connector (All connectors of the same type would be mounted in the same orientation if possible). We would select the left connector on the chamfered side and indicated it with a white rectangle on the Silk screen around the pad Pin '1' as shown below,

Panasonic would not tell its customers what pin is 1 on a part like this as different companies have their own design rules they like to follow.