3B a:B+K DNK 2K is 73-74 damage and is character and range specific. The minimum range differs for each character. You can make it more consistent by buffering 665 after 3B to do a small dash forward before doing a:B+K. Buffering 66 is faster than 6 for very short distances and long distances (in neutral, 6 is often better due to input time, but that isn't a factor when you buffer). How much time you have to do this also varies by the character, and you get less time on side hits but you are usually closer than normal in those situations anyway since their body length isn't pushing you out. Staggering the timing of the DNK hits is required sometimes, and you want to space out the hits as much as you can in general to carry them as far as possible.
Characters that it works on at almost any range, especially if you 665 a

ZWEI, Hilde, Tira
Characters that it only works if you're right in their face and do a well-executed 665 a

Maxi, Siegfried, Algol (super hard)
Doesn't work on at all, unless you spike them into a stage boundary:
Aeon, Astaroth, Nightmare, Cervantes, Voldo, Ivy, Edgemaster
So to help remember, it works well on all the girls and skinny dudes, except Ivy and Maxi.
It doesn't work on big or evil guys. Or Siegfried or Edgemaster.
A final note on GI: you have time to move forward before 3Bing while staying within the 27 frame window. This helps get the full damage, making Yoshimitsu's post-GI pretty strong.