Hi Bhargavi,
Are you having API Portal? If so there are reports which can be generated per developer. If you have only API gateway, i am not sure if you can get it directly.
One way I can think of is to use Query Throughput Quota Assertion. This assertion would load the count into a variable. To make use of this assertion, we have to setup a custom counter using Apply Throughput Quota Assertion. Please look into documentation for more details.
Thanks,
Abhishek