Hi
You have to identify needs and expectations of interested parties.
Eg. Customer need is to follow AIAG PPAP4th editon manual
If it is met, you can consider they are satisfied.
Apart from that data such as complaints from interested parties, etc. can be collected and monitored to check whether they are satisfied or not.
And 9.3.2 C.1 requires to monitor
customer satisfaction only. Feedback (complaints/suggestions) are to be monitored from interested parties.
You can maintain a complain/suggestion register / suggestion box or any forum where interested parties can give suggestions or register complaints.

Thanks,
Amit Ballal