Andorra - 2 co-princes. (But note that the position is not hereditary, but ex-officio; the co-princes are whoever is Bishop of Urgell, and whoever is President of the French Republic. And it’s a position, not a title; a co-prince is not, e.g. “Prince Emmanuel”)
Belgium - Wikipedia lists 6 living princes in the Royal Family, plus I suppose you could argue about the ex-King, though he still has the title “King”, not “prince”.
Denmark - Wikipedia lists 7 living princes. In addition, the male members of the deposed Greek royal house are princes of Denmark as well as of Greece; if you want to count them there are I think 7, plus the current pretender to the Greek throne, King Constantine II, who is a Prince of Greece and Denmark, though he doesn’t use the title. The Duke of Edinburgh was also a Prince of Greece and Denmark, but he renounced the title on his marriage. (He counts as prince of the UK, though.) Say 14, not counting the putative King of Greece or the Duke of Edinburgh.
Lichtenstein - there’s the reigning Prince, of course, plus Wikipedia lists 9 of his descendants with the title “prince”, and 11 living collateral relatives with the title - a total of 20
Luxembourg - the Grand Duke and his heir do not use the title “prince” but other male members of the Grand Ducal family do - 17 of them.
Monaco - there’s the reigning prince. Other legitimate members of the family are “prince” or “princess”; currently only 1 has the chromosomal qualifications to be a prince.
The Netherlands - currently 5 princes in the royal family, according to Wikipedia, plus 1 who lost the title when he married without parliamentary consent. We can’t count him.
Norway - just 2; the Crown Prince, and his son.
Spain - the monarch’s eldest child, if male, would be “Prince of Asturias”, but there is currently no Prince of Asturias, since the King’s eldest child is female. (She is “Princess of Asturias”.) If the King had any other sons, each would be an “Infante of Spain”, and this title is generally regarded as equivalent to “Prince”. But the present King’s only other child is also female. If the Princess of Asturias had sons, they too would have the title of “infante”, but she’s only 13 years old. And similarly the living descendants of former kings who would be “infante” if male all lack the required chromosomes. So, no princes in Spain just now.
Sweden - Wikipedia lists 6 members of the Royal Family with the title “prince”.
UK - By my count, 11 current princes, although some of them are also Dukes and this title is generally used in preference - e.g. Prince Phillip, Duke of Edinburgh, is generally just referred to as the Duke of Edinburgh. The Wessexes have a son who is entitled to the title, but he doesn’t use it; so we won’t count him.
So, I make that 86 princes either reigning in Europe or members of reigning European houses, if we count the Greeks as princes of Denmark also, and if we disregard former princes now using the title “King”, and if we counting the co-princes of Andorra. Obviously, you could argue about all of those. Over 40% of European princes are accounted for by just two states - Luxembourg and Lichtenstein.