It is possible to see the number of times a URL monitored by Synthetic had calls

[Alchemy]

Good morning.

I have some URLs monitored in Synthetic in HTTP Monitor mode, it would be possible to see the number of times it was requested by users.
If you do not have this possibility using HTTP monitoring mode, it would be possible using Browser monitor

I'm trying to do this search using Data Explorer, but if not there, where would it be?

[HannahM]

HTTP Monitors make the request to a url that you configure it to. It is not related to real users. If you want to see how many times a real user visits that url then it sounds like you are interested in Real User Monitoring. You can also do this using Dynatrace. 
Real User Monitoring Docs

There's also videos on Real User Monitoring in the University. This course might be a good start point