Yes, you can file RTI to Punjab National Bank (PNB) .
Punjab National Bank is a Public Sector Undertaking working under Central Government of India regulated by Reserve Bank of India Act, 1934 and Banking Regulation Act, 1949. PNB is a "Public Authority" as per Section 2 (h) of the RTI Act 2005.
You can address the RTI Application to the concerned "Public Information Officer (PIO)" of the Bank Branch, Regional Head Office, Headquarters as the case maybe by paying the prescribed fee. You can file the RTI Application either Online or by Offline mode.
To know more about the procedure to file RTI Applications Online for Central Govt. Departments, please refer https://onlinerti.com/how-to-file-rti-online-for-center