Analyze > Descriptive > Cross-tab
Put mouth cancer into column
Put gender into row
Click "Statistics", select "Chi-Square"
Click OK and then OK again to run the test.
Look for the chi-square test output. If the two-tailed p-value is less than 0.05, it means either:
1) The proportion of answers in mouth cancer differs by gender, or
2) The proportion of gender differ by their knowledge about mouth cancer.
(It's strange this way, because Chi-square does not specify which is exposure and which is outcome, both of these results go hand in hand, you can just report the first one.)