I added a shape file of Iran to Qgis.
'Tehran' has 35.6833° N, 51.4167° E coordiantes, however Qgis shows Tehran with 4772860,31296767.
How i can view coordinates of a city or location in latitude and longitude form in qgis?
Simpliest way is to set EPSG:4326 as Project CRS and check on-the-fly projection. If Qgis recognizes the CRS information in the shapefile, it wil place it in the correct position.
Please note that project CRS and layer CRS can be different, and have to be in your case.
You need to know the coordinate system/projection of the projected data in order to unproject it back to decimal degrees.