How to get all specific fields from one ACF Group?

U can use get_fields() which return all fields from current page.
Additionally you can filter array checking which key matches.

Example:

$questions = get_fields();
$questions_array = array_filter($questions, function($key) {
    return strpos($key, 'question') === 0;
}, ARRAY_FILTER_USE_KEY);

foreach( $questions_array as $question) {
 // your code here
}