The phrase "ascertain exactly" is correct and usable in written English.
It can be used when you want to emphasize the need to determine something with precision or accuracy.
Example: "We need to ascertain exactly what the client requires before proceeding with the project."
Alternatives: "determine precisely" or "establish exactly".
I rang a journalist friend in Beijing to ascertain exactly what had happened.
"Everyone is just trying to ascertain exactly what's happened," he said.
How to ascertain exactly when this happens may be a point still to be negotiated.
But the relief was suspended until further calculations could ascertain exactly how well the levels matched.
He also said they would be unable to ascertain exactly whose device the website had come from.
"It is impossible to ascertain exactly how much of Teva's product has entered or may enter the market," he said.
While reading Anne Trubek's essay "What Muncie Read" (Nov. 27), I wondered by what criteria she deemed a found library ledger more fruitful in ascertaining exactly what people read than "diary entries or sales figures".
In the years following, the government never ascertained exactly what transpired on the Gulf of Tonkin that night of August 4, when the supposed second attack took place.
"We'll be working with him and our officers will be interviewing him and ascertaining exactly the circumstances and the context around why he would make such, such, these comments".
In addition to this theoretical uncertainly, there is also considerable practical uncertainty in ascertaining exactly which panels were used in each study, especially in studies where more than one panel was used.
Although ascertaining exactly how or when the person acquired his infection was not possible, he did report having been bitten once and scratched on a number of occasions by macaques at Sangeh.
