We are filing pension paperwork. It wants our tax code - where do I find that?

If you are entering a Form 1099-R for pension income there is no such entry for a tax code.  You do have to enter the PAYER'S TIN which is a nine digit number.

Where are you being asked for a tax code?

Are you entering a 1099R?   There is a code in box 7.   It is usually a code 7 in box 7 so it might be confusing.   Do not try to enter your retirement amounts without having the actual 1099R.   You need other info from it.   

Or are you filling out the paperwork to start receiving your pension?   Ask the plan what they want.