选So I have还是So I do?

have是助动词.
这种句型要看原句里有没有助动词,如果有,就用原句里的助动词.
--I will go there tomorrow. (助动词will)
--So will I.
--I have finished my homework.(助动词have)
--So has he.
没有助动词的话,就要用do系列了,当然还要考虑时态.
--I hate milk.
--So do I.
--He didn't go there.
--Neither did she.