The part of the sentence "a key question that" is correct and usable in written English.
You can use it to introduce a question that is important to the topic you are discussing. For example: "A key question that needs to be addressed is whether or not providing free healthcare to everyone is feasible."
It highlights a key question that is still to be answered: how should gaming disorder be defined?
I believe that a key question that has not been addressed, but is central to the controversy, is: how to use the Web as a teaching platform appropriately?
"This is a key question that has confounded us," said the CDC's Dr Nancy Messonnier, who is overseeing the agency's outbreak investigation.
As countries seek to adopt cleaner energy sources, a key question that is often asked is what the avoided emissions from the switch to non-fossil based energy sources are.
A key question that had to be answered in the early days of telecommunication was how best to maximize the physical plant in particular, how to transmit the maximum number of telephone conversations over existing cables.
The ignorance of this cover highlights a key question that is not – in the current climate of frenzied analyses of Egypt – being asked: is it more democratic to elect a dictator or to topple one?
But what counts as an "ill effect" and how to demonstrate it is a key question that belongs to the how of politics that algorithmic regulation wants to suppress.
Once you've done all that, you'll be well enough informed to agree or disagree with the seeker on a key question that is seldom asked: What role should you play?
But these changes raised a key question that wasn't clearly answered in the law.
A key question that remains unanswered of course is whether the service will succeed financially.
A key question that arises from the observed similarities between genetic changes in hPSCs and cancer cells is whether adapted hPSCs exhibit similar malignant properties to cancer.
