Q: What is the proper way for a bishop to give the blessing with the monstrance at the end of eucharistic adoration: Does he bless the people one time or three times?
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A: The Ceremonial of Bishops describes this action in #1114, where it says that the bishop “makes the sign of the cross over [the people] with the monstrance, in silence.”
At the conclusion of Mass, the Ceremonial says explicitly “he makes the sign of the cross three times over the people” (#169).
I conclude from this that due to the absence of the words “three times” in Latin and in English in #1114, that a bishop holding the monstrance at the end of adoration makes the sign of the cross once over the people.