Hello Knicksyanks,
Thanks for choosing the Apple Support Communities. If we understand correctly, you are looking for info on how to identify what number is being called on your iPhone with Dual SIM.
When a call is received you should see a letter in a box below the name of the person or number that is calling. This icon corresponds with the first letter of the label you assigned to the phone number receiving the call. Each of the phone lines would've been assigned a label, for instance "Primary" and "Secondary." If the call is received on the "Primary" line you should see a "P" icon. Likewise you would see an "S" icon for the "Secondary" line. You can change the labels that are currently associated with the lines if you choose to do so.
You can find out how to make changes to the labels, as well as an example of what the icons should look like for an incoming call in this video: How to set up and use Dual SIM on your iPhone — Apple Support - YouTube
To just see the incoming call information you'll want to skip ahead to the 2:45 timestamp.
Cheers!