Dial 199 from your Jio SIM and ask for your number
Open the MyJio app and check your registered mobile number
Send an SMS or missed call from your Jio SIM to another phone and see the number on that phone
Check the SIM card pack or welcome letter if you still have it
Go to a nearby Jio Store or Jio service center with valid ID proof
Check your phone settings under SIM status or About Phone
Use the Jio website or MyJio login with your registered details if already linked
Call another number from your Jio SIM if outgoing services are active and note the caller ID displayed