Use business speaking when you're naming workplace speech as a skill or field. Business speaking is what that workshop teaches.
This pattern is drawn from how related workplace-English phrases behave; direct evidence for business speaking itself is thin.
When a reader means the whole field, not the skill
If you're naming the skill or field, the phrase fits. Her course covers business speaking, from updates to negotiations. Here it names an area of training, not one event.
Writing a resume line or workshop agenda? The phrase works there too, because it still names the skill. The session builds confidence in business speaking.
Self-introducing? I teach business speaking names your field, while I gave a presentation this morning describes your day. One is a label, the other an event.
Reporting a single meeting? Swap the phrase for what actually happened. She spoke calmly about the delay in the meeting works; she did business speaking in the meeting sounds odd, because it labels a scene rather than a skill.
Quick check: write one sentence using business speaking for a skill, then one about an actual meeting. If your second sentence needs to report what happened in the room, you've found the boundary.
One qualifier that changes the wording
The qualifier to watch is a single-event time marker like this morning or yesterday. I teach business speaking stays natural, but I did business speaking this morning sounds odd, because the phrase names a skill, not something you finish in an hour.
The verb decides it. A skill label pairs with ongoing or habitual verbs, so she's been practicing business speaking or he wants to improve his business speaking hold up fine even with a time span like this year.
A one-off time marker forces the event reading instead. When that happens, say what actually occurred: she presented the quarterly figures yesterday, not she did business speaking yesterday.