Currently the best forum is at http://stackoverflow.com. You can also reach out on mailing lists or IRC chat. The following is a list of mailing lists:
- Scikit-learn: https://lists.sourceforge.net/lists/listinfo/scikit-learn-general.
- NumPy and SciPy mailing list: https://www.scipy.org/scipylib/mailing-lists.html.
IRC channels:
- #scikit-learn @ freenode
- #scipy @ freenode