Community Answers has built in module positions where you can publish your ads and modules. This gives great flexibility to insert your custom content/ads without hacking the core. Here are the available module positions (names self explanatory)
Listing Page
questions-list-above-list: Displays the module above the questions list
questions-list-below-list: Displays the module below the questions list
questions-list-after-question-X: Displays the module in questions list after question X, where X is the position of question in list. e.g. questions-view-after-question-1
questions-list-above-ask-form: Displays the module on top of the ask form
questions-list-below-ask-form: Displays below the ask form
View Question Page
answers-view-above-ask-form: Displays above question form but below the toolbar
answers-view-below-question-details: Displays after the question description/details but before answers
answers-view-below-question-replies: Displays after the question replies but above ask form
answers-view-after-answerX: Displays after answer X where X is answer number start from 1