Paypal Recurring Payments ("subscriptions") - user specified amount?

Can we make user specified amount for Paypal recurring payments ?

Yes, you can have user specified amounts in the recurring payment option. Please take a look at the following guide first on how to set up recurring options:

https://www.jotform.com/help/166-How-to-setup-a-recurring-payment-option

When you are setting up the subscription, please select the Variable Price option, and then select whether your users will be entering the custom amount manually, or you wish to pass it from a calculation field:

This will result in your form having a variable input field for subscription price:

If you need further assistance, please let us know.