I have left 13 roza of month of Ramazan of last year. Now I am going to Ziaraat e Karbla (Iraq) and Iran. In Mafati ul Jinan in Bab ul Ziarat it is mentioned about the important things to do before ziarat. One of them is to have Roza for 3 days before going to ziarat. Can I observe such roza (fast) as I left 13 Wajib Roza of Ramazan

Yes if you have your qaza roza remaining then you have to complete them before having mustahab roza but there is one way. You fast three days with the niyyat of your wajib left roza before going to ziyarat. Inshallah you will get both sawab of your mustahab fast and other side your three wajib fasts will also be done.