You should know the basics of point-set topology and the content of the course Algebraic Topology 1 (see Algebraic Topology I ).
Useful to have is a basic knowledge of the fundamental group and covering spaces (at the level usually covered in the course "topology"). Students not familiar with this topic can look this up, for example in Chapter 3, Section 1-6 and Section 8 in G. Bredon, "Topology and geometry", Graduate Texts in Mathematics, 139. Springer-Verlag, 1997. (Members of ETH can legally download the ebook trough the ETH network.)
Some knowledge of differential geometry and differential topology is useful but not necessary.
Some (elementary) group theory and algebra will also be needed.