How many times did Jesus say Verily Verily I say unto you?

Twelve times (in the King James translation; more modern translations use "to" rather than "unto"):

Matthew 5:22, 28, 32, 34, 39, 44 (within the Sermon on the Mount)

Matt. 11:22, 24

Matt. 12:6, 36

Matt. 17:12

Matt. 26:29