Question

How do I find the number of sigma and pi bonds in a molecule?

Answer 1

Sigma is the first bond, or a single bond. Pi bonds are the second bond in a double bond, or the second and third bond in a triple bond.
Cl-Cl is a single bond, one sigma bond
O=O is a double bond, one sigma bond, one pi bond
N=N is a triple bond, one sigma bond, two pi bonds
K-O-H has two sigma bonds
H-C-N (there is a triple bond between C&N) has two sigma bonds, and two pi bonds.