It all seems to be around 30% though (excepting Germany, where support is only a third for young Germans). The Romanian article you posted suggests around 30% would vote to restore the monarchy. Between 30% and 40% of Serbians would. Around a third of Russians and a third of young Germans:
Restored monarchy gains young Germans' support - The Local
Tsar-fetched? Almost a third of Russians favor return of monarchy ? RT Russian politics
B92 - News - 39 percent of Serbians in favor of monarchy, poll shows
Restored monarchy gains young Germans' support - The Local
Tsar-fetched? Almost a third of Russians favor return of monarchy ? RT Russian politics
B92 - News - 39 percent of Serbians in favor of monarchy, poll shows