Question might be a bit obscure. The yield of the 10-year treasury note is reported daily on TV and in the papers. Since there are notes with different maturities in circulation, also more importantly, different coupons, which particular 10-year note does the daily yield refer to? The notes auctioned on Jan 1, 2018, Jan 1, 2017, February 35, 2010?
It will depend on the source, but if they're just referring to the yield, I think it's usually the most recently auctioned bond (this is what Bloomberg quotes if you don't override anything, and Bloomberg is likely the source that the TV stations at least are getting it from). Right now (June 22, 2018), that's the one which matures May 15 2028 and has a coupon of 2.875.