It's a little tricky to work this out without knowing a) your intention and b) the schema of the tables involved. Why do you need the add-ons table in the query twice?
Maybe this will work?
$query = "SELECT *
FROM " . $CFG['table']['menuaddons'] . " m
INNER JOIN " . $CFG['table']['addons'] . " t1 ON m.addonparentid = t1.id
WHERE m.addonparentid = " . $parentid . "
ORDER BY t1.addonsort DESC";
If not, please post more information. Once you have it working, please consider converting this to using PDO - the current query is vulnerable to SQL injection, depending on where the variables come from.