Yes, you can use WhatsApp in Jio Phone 2.
Jio Phone 2 does have the plastic keypad.
Yes, Jio Phone 2 does support the Punjabi language.
Yes, Jio Phone 2 comes with pre-loaded FM radio. You can even record songs which are broadcasted on FM radio.
Jio Phone 2 does have the 4GB internal memory. Practically, it has unlimited contact book.