how many catholic priest got killed during WWII?

Answer 1

I haven't found numbers for world wide but here is some data on the 2,801 members of the Polish clergy who were killed in WWII:

Zenon Fijałkowski, Kościół katolicki na ziemiach polskich w latach okupacji hitlerowskiej (Warszawa: Książka i Wiedza, 1983), provides the following synopsis at page 375:

During the Nazi occupation, the Catholic Church in Poland experienced enormous clerical and material losses. According to the latest research by W. Jacewicz and J. Woś, in the years 1939–1945, 2,801 members of the clergy lost their lives; they were either murdered during the occupation or killed in military manoeuvres. Among them were 6 bishops, 1,926 diocesan priests and clerics, 375 priests and clerics from monastic orders, 205 brothers, and 289 sisters. 599 diocesan priests and clerics were killed in executions, as well as 281 members of the monastic clergy (priests, brothers and sisters). Of the 1,345 members of the clergy murdered in death camps, 798 perished in Dachau, 167 in Auschwitz, 90 in Działdowo, 85 in Sachsenhausen, 71 in Gusen, 40 in Stutthof, and the rest in camps such as Buchenwald, Gross-Rosen, Mauthausen, Majdanek, Bojanowo, and others.

With love in Christ.

Answer 2

I'm sure that many did. Millions of people were slaughtered in this vile war.
While I don't have any statistics on it, you may be well served in writing the Vatican. They certainly will have some idea.