How are bank routing numbers structured in Pakistan?

Pakistan does not use the routing number per se. We have two local schemes, somewhat convoluted. We have each bank designating their own account number and branch code, the length and format of these vary from bank to bank. Then we have the IBAN which is standard.

For an international transaction, depending on where the transaction is originating and what network is being used, the routing code can vary. Best to ask the beneficiary or the bank itself.