Nani Ji (ਨਾਨੀ ਜੀ) - This is the most common and respectful way to address your maternal grandfather.
Other options, depending on the context, could include:
* Nani (ਨਾਨੀ) - A slightly less formal way of saying "maternal grandma"
* Nana (ਨਾਨਾ) - This word is specifically for "maternal grandpa" but it is less common in everyday language.
* Naana Ji (ਨਾਨਾ ਜੀ) - A respectful way to address your maternal grandfather using "Naana."
Ultimately, the best way to refer to your maternal grandfather in Punjabi depends on your personal relationship and the specific context.