Yes it will usually tell you to taunt at a given stack or when something happens (like other tanks diamond breaking on Opulence). The stack given is USUALLY the amount that you can, at minimum, taunt on and not clip stacks. Like 7 I believe for JFM it will tell you to taunt.
“Crushed on Tank, Taunt now” in big blue letters on my screen after bestial smash.
I use a weakaura for taunt swapping on Opulence.
DBM usually warns me but most of the time i ignore it and use other cues.
Think its actually 6, but its been a while.