您好，My parents often visit my grandma on Sunday. 的特殊疑问句需要根据（问什么）而定：
1）对主语提出（谁）拜访 grandma
Who often visit your grandma on Sunday?
My parents often visit my grandma on Sunday.
2）对宾语提出（谁），也就是父母亲拜访谁
Who do your parents often visit on Sunday?
My parents often visit my grandma on Sunday.
3）对时间提出疑问，也就是什么时候拜访
When do your parents often visit your grandma?
My parents often visit my grandma on Sunday.
4）对拜访的频率提出疑问，也就是多频繁地拜访一次
How often do your parents visit your grandma?
My parents often visit my grandma on Sunday.