The LORD said to Moses, "Tell Aaron and his sons, 'This is how you are to bless the Israelites. Say to them:The Wikipedia article on Birkat Kohanim is worth reading. One highlight:
" ' "The LORD bless you
and keep you;
the LORD make his face shine upon you
and be gracious to you;
the LORD turn his face toward you
and give you peace." '
"So they will put my name on the Israelites, and I will bless them."
In the case where no Kohanim are present in the synagogue (but there still is a minyan) the hazzan will read the prayer verse by verse, and the congregation will respond after each verse with "kein yehi ratzon, may it be God's Will." This response is used instead of "Amen," because the hazzan is merely "mentioning" the blessing, as it were, and not actually performing the ritual. However, many congregations (including Chabad) do indeed respond "Amen." This response is also employed on days and times when the Amidah is publicly repeated but the Kohanim do not recite the priestly blessing.(For the holidays, I received Leonard Cohen's Live in London DVD from a good friend.) So, in closing, here's one famous Cohen giving the Birkat Kohanim:
Do you have any Kohanim in your congregation? If so, do they pronounce the Birkat Kohanim?
Post-note: please don't take this post as a criticism of non-Cohen leaders or congregations employing this blessing; I really am grateful when anyone pronounces a blessing over me! By sharing the quotation from the Wikipedia article, I actually wanted to highlight the creative yet simple way that Jewish practice manages to preserve the priestly responsibility to carry out the mitzvah of Num. 6:22-27 without forbidding communities who don't have any Kohanim from employing this wonderful blessing as well.