Technically, you could create a custom vulnerability that would match "normal" DNS traffic, set it to Alert for the action and set packet capturing to on. Unless you have plenty of resource overhead available to use on your PA I'm guessing this could be a bad idea for that much packet capturing just the same. It would fill up threat log quota or Extended Threat Pcaps quotea much more rapidly. In the logging then you would get a request source and destination just having to open the PCAP to get the domain record that was requested. It would be great if there were just a DNS lookup log with the requestor IP included. Perhaps on your DNS server this is done and you can limit DNS lookups to just your DNS server(s) so everyone would need to be pointed there.
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