The phrase "about to demonstrate in" is correct and usable in written English.
It can be used when indicating that someone is on the verge of showing or explaining something in a specific context or setting.
Example: "I am about to demonstrate in detail how this software works."
Alternatives: "ready to show in" or "preparing to demonstrate in".
This semester's students were about to demonstrate their wizardry skills in front of an audience of parents.
This stage of my career was about to demonstrate another important lesson in communicating ideas.
Despite a weeklong school break, about 1,000 students turned out to demonstrate in front of the 17th-century Senate building.
We expect these companies and others like them to do more than simply talk about sustainability; we need them to demonstrate, in their core activities, that their commitment is real.
Whereas Brazil has demonstrated its superiority in sugarcane-based ethanol, Argentina is about to demonstrate its superiority in soy-based biodiesel.
Still, the authorities say they are not so worried about groups that have city permits to demonstrate in seven official protest zones at the edge of Olympic events.
Or, with a little close reading, couldn't overlook how very aware the Merkel government is of the embarrassing aspects of seeming to tighten links to Russia at a time when Moscow is about to demonstrate how far in the last decade it has retreated from democracy.
They are standing at the front of the restaurant, beside an oak wine barrel attached to a small bottling machine, and are about to demonstrate a crucial step in the making of a new kind of Montlouis: a thoroughly dry, gently sparkling wine officially named Pétillant Originel but often called by its makers Pétillant Naturel, or more affectionately, Pet'Nat.
Mr. Rajoub refused to go for several days, and the wrangling continued today, with about 300 officers demonstrating in Hebron in favor of their old boss.
The best way to talk about your evidence is to demonstrate it in a story.
