You only need a table name on a collumn if you are using JOIN, to distinguish the table. And even then you should asign it a value, " . TABLE_PREFIX . "user AS user, so you wouldn't need the prefix more than once.
In this case, you don't need the table name to be attached to the collumn at all.
Code:
SELECT timezoneoffset
FROM " . TABLE_PREFIX . "user
WHERE userid =