The word "expertness" is not an accepted word in written English.
It is not found in most standard dictionaries. The word you are looking for is "expertise". You could use "expertise" in a sentence like this: "He demonstrated his expertise in the field of programming."
Once I'd offered the engineer a seat at my desk and pointed the reading light in the right direction, removing the duffed-up screen on the iPhone 5s was done with care, precision and a deft expertness which would have defeated me in seconds had I even known where to begin.
The expertness of the work may be attributed to Jenson's training as a medalist before becoming a printer.
Her novels feel English in their matter-of-fact expertness, their quickness to set a large cast of characters in motion, their disinclination to moralize, and their subordination of psychological and natural detail to a colorful social weave.
There is always the impression of craftsmanship, expertness, as the underlying source of it all; and they are not enough".
The problem, thought Trewin, was that this worked against the drama itself: "While we are observing the fidgety expertness, the devices of a man of the theatre, we cannot also believe that we are hunting whales in the Pacific".
Filmed with an analytical expertness and a devout attention to the continuity of action in long takes at discerning angles, the fight is also presented in its existential purity — there's no television-style commentary accompanying it, no music added, no slow-motion or instant replay, nothing but the live sound of the fight and the crowd.
I had of Père de Vaux, in his different department, an impression somewhat similar: intellect, expertness, fortitude, tenacity, an element of daring, and what now seems so rare in France effectiveness.
"The directness of the concept, the expertness of the plan and the quality of execution are commendable," Ada Louise Huxtable, then the architecture critic of The New York Times, wrote in 1963.
