'have full command of' is correct and usable in written English.
It means "to be completely knowledgeable or have complete control over something". You can use this phrase in both formal and informal contexts. Example sentence: My supervisor has full command of the software, so he can help us if we have any questions.
He also has full command of the most efficient White House political machine in recent memory.
But the motivation for his actions and whether he had full command of his mental faculties are apparently in question.
There is no question, on the bench or in chambers, that she has full command of the complex legal issues that reach the court.
For her Rio is the fulfilment of a wish that had a different focus five years ago when she had full command of all her limbs, a Commonwealth Games silver in her pocket and London 2012 was the target.
President Trump had full command of the news cycle; Republicans, who had passed multiple ACA repeal bills, insisted that they had a plan to scrub the act off the books.
"He's a crafty left-handed guy who has full command of his pitches," said Newbury Park Coach Scott Drootin, whose team beat Skaggs, 3-0, in March.
He isn't the most physically gifted, but he has full command of coach Art Briles' super dangerous offense, throwing for 4,200 yards while accounting for 46 touchdowns last season.
Steinhaus had full command of several foreign languages and was interestingly, known, for his aphorisms, to the point that a booklet of his most famous ones in Polish, French and Latin has been published posthumously.
It came at the end of a daylong hearing in which prosecutors described mass killings, torture and rape in distant mountain villages almost 30 years ago and stressed that Mr. Ríos Montt, a former general, had full command over his troops and knowledge of their actions.
