How can we get to know how many times a user has purchased the consumable product?
@surendra019, the transaction report you can get from the developer dashboard gives the user_id with each transaction. You'd have to analyze the data yourself and to go back to the beginning of time would require all the reports. You can also get the same information from the push notifications if you've saved them all. If there's another way, I'm not aware of it.
If you're asking how to do it from within an app, that's a different matter. I believe you just use GetAllPurchases.