Where can I look for post-doctoral positions in Europe?
More information is always helpful.  Most students who do postdocs find them in the following ways.

1) A recommendation to a company or university from the faculty of their current institution.

2) A recently graduated Ph.D. student who may know of a great fit for you at their new postdoc.

3) A place you've interned in the past that is open to bringing you on as a postdoc.

4) University mailing list for graduate students in your field.

5) Your academic network you build from all those years attending conferences and presenting your work.