The opening verb should be "have" -- plural.
Student or Learner
what is wrong with this sentence?
Has any of the witnesses been sworn in yet?
'Has anyone of the witnesses been sworn in yet?'
Is it correct?
You could ask "Has anyone been sworn in yet?"
True, but you can't pair 'anyone' with another noun/pronoun.
If you want to specify witnesses, you'll have to use the "Have any of the witnesses" construction.
Aside from the jurors, who take their oath as a group before the trial begins, witnesses are the only other people sworn in, as far as I can recollect.
***** NOT A TEACHER *****
You may be interested in what one expert says:
"When any ... [is] followed by of + plural, [it] is usually used with singular verbs in formal style in British English. Plural verbs are common in informal British usage and generally in American English."
-- Michael Swan, Practical English Usage (1995 edition), entry (NOT page) 509.5.