I am a EU citizen and from September onwards I will pursue an llm in european and international tax law and I wonder what are the prospects regarding finding a job in the field of taxation besides working in one of the Big 4 ?
Are there job opportunities in international organizations or in eu bodies?

I'm sure there are jobs in those kinds of organizations but those are probably fewer than what's available at the Big 4 and other large accounting organizations. You can probably take a look at job boards and on these organizations' websites to see how much tax help they actually hire. My guess is not very much.

However, different countries might have different rules in terms of who can provide tax law consulting. You'll probably have to look at the laws for the countries where you are looking.