If you choose nonparametric ANOVA, the Multiple Comparisons tab lets you choose:
• No multiple comparisons
•Compare the mean rank of each group with the mean rank of every other group
•Compare the mean rank of each group to the mean rank of a control group you specify
•Compare selected pairs of columns.
In all cases, you won't have any choice of method. Prism will use Dunn's method at a significance level alpha you choose (usually 0.05).