Looking on the internet deeply has found these results:

I don’t know what to say is the most popular phrase on the web.

I don’t know how to say 195,100 results on the web	I don’t know what to say 116,900,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
I Don't Know How To SayYouTube · 168 videos Play all Popular Videos Oct 22, 2014 ... Ion Ludwig 「I don't know how to say it in English.」の部分一致の例文検索結果. 該当件数 : 1件. 例文. I don't know how to say it in English. 例文帳に追加. 英語で何というか分かりません。 I Don't Know How To Say This Lyrics. New! Highlight lyrics to add Meanings, Special Memories, and Misheard Lyrics... Submit Corrections Cancel. God only knows what I would say to you. You'd hear just some scattered parts of words I'd ... Ion Ludwig "I Don't Know How To Say This". God only knows what I would say to you. You'd hear just some scattered parts of words I'd mumble to you, Of words I'd mumble to you. I thought that at first it would be good for me. I've come to find out that I just ... I Don't Know How To Say. Darween ... 50+ videos Play all. Play now. Mix Weblio Email例文集 ...	It doesn't look like this phrase is very popular! The search could not find any examples on the internet.

I don’t know how to say

195,100 results on the web

I don’t know what to say

116,900,000 results on the web

More popular!

I Don't Know How To SayYouTube · 168 videos Play all Popular Videos
Oct 22, 2014 ... Ion Ludwig
「I don't know how to say it in English.」の部分一致の例文検索結果. 該当件数 : 1件. 例文. I don't know how to say it in English. 例文帳に追加. 英語で何というか分かりません。
I Don't Know How To Say This Lyrics. New! Highlight lyrics to add Meanings, Special Memories, and Misheard Lyrics... Submit Corrections Cancel. God only knows what I would say to you. You'd hear just some scattered parts of words I'd ...
Ion Ludwig
"I Don't Know How To Say This". God only knows what I would say to you. You'd hear just some scattered parts of words I'd mumble to you, Of words I'd mumble to you. I thought that at first it would be good for me. I've come to find out that I just ...
I Don't Know How To Say. Darween ... 50+ videos Play all. Play now. Mix
Weblio Email例文集 ...

It doesn't look like this phrase is very popular! The search could not find any examples on the internet.