I am studying for my Bar Mitzvah. My siddur (Mishkan T'filah) says from the Haftarah blessing: יִתְבָּרַךְ שִׁמְךָ בְּפִי כָל חַי, but my practice sheet says יִתְבָּרַךְ שִׁמְךָ בְּפִי כָּל חַי! Do I say chol or kol?
I checked Artscroll, Koren (a machzor, but that shouldn't matter), Sim Shalom (used by Conservative), Tehilot Hashem (nusach Ari, used by Chabad), and Gates of Prayer (older Reform siddur). All have כָּל.
The OP then said in a comment that the siddur in question is Mishkan T'filah, the current Reform siddur. I just checked that and, sure enough, the Hebrew has כָל. However, everything in that siddur is transliterated and the transliteration says kol, not chol, so one of these is a typo:
The repeated gutteral sounds of כָל חַי sound odd to my ear. I can't say nobody does that because I don't know everybody's customs, but my strong suspicion is that you want כָּל. You should verify this with your rabbi.
If you are Ashkenazi, having the words כָל חַי next to each other sound weird because the khaf and the chet have the same pronunciation amongst Ashkenazim, and i think it sounds weird to them. This isn't an issue amongst Sephardim who distinguish between chet and khaf.
The reason i bring up the sounding weird is because i have no idea why anyone would grammatically make it כָּל חַי. Most times when you have a word that ends with an open vowel with a yod, the word that follows it is robbed of its dagesh. An example would be the blessing from the Amidah
"מֵבִיא גוֹאֵל" It would normally be "גּוֹאֵל" but the gimmel loses its dagesh because of the word מֵבִיא. So in my humble opinion, it should be כָל חַי. But maybe the authors of the siddurim changed the spelling on purpose because of how weird it sounds to them and Ashkenazim in general. So it's up to you, if you want to follow the rules of dikduk, go with כָל חַי. But if you want to go with what your community does, then do כָּל חַי.