Can I measure the RPM and see it somewhere on the app or is there a simple method to measure instantaneous rpm of the SPARK?

There is no fix RPM of the motors of a quadrocopter. The motor speeds are highly variable. You can hear it when you climb your Spark how the motors increase in speed.
It would not make any sense to display it in the app.
If I may ask....why do you need that information?

Cheers,
Wolferl