Dear Ms. Vendel, dear SIG,
The address on the postcard gives the "V." (=5th) district of Budapest, which before the war included both Lipotvaros (Leopoldstadt) and to the north of it what is now called Ujlipotvaros (New Lipotvaros).
Later Ujlipotvaros was separated out with the border between them drawn along what is now Szent Istvan Korut (formerly Lipot Korut)/Margit hid.
Pozsonyi utca in then District V. existed before the war, too. It is a logical name, as the street leads >from the center of Pest towards the basic direction of Bratislava (Pozsony).
Ujlipotvaros is now in the 13th district. So, you will want the address: XIII. ker. Pozsonyi ut 20.
I don't know what the second "v." in the address means, however.
Greetings >from Prague,