AFAICS Question2Answer has pagination already built into the code that fetches questions, so you're probably better off running your own queries via the function qa_db_query_raw() (located in qa-include/qa-db.php). All posts are stored in the table qa_posts (questions with the type "Q," answers with the type "A," and comments with the type "C").
To get a list of all questions with their ID and title from the DB you could run something like this:
$query = "SELECT postid, title FROM qa_posts WHERE type='Q'";
$result = qa_db_query_raw($query);
Use the methods of the resulting mysqli_result object to retrieve the data, e.g.
$questions = $result->fetch_all();
which will return the entire data set as a jagged array (i.e. an array of arrays).