get it vs get on to

get it

verb
  • Used other than figuratively or idiomatically: see get, it. 

  • To get what's coming to one: to feel someone's wrath; to receive punishment; to receive a retaliation; to receive a beating. 

  • To have sex, especially referring to its possibility or eventuality. 

  • To understand something, to catch on. 

intj
  • Used to encourage someone, especially to indicate that someone is doing something well. 

  • Used to draw attention to a pun or other joke one has made. 

  • Do you understand? Have you heard? (after explaining or giving an order) 

get on to

verb
  • Used other than figuratively or idiomatically: see get on, to. 

  • To contact (someone) in order to raise or discuss a certain matter. 

  • To progress to; to start working on. 

How often have the words get it and get on to occurred in a corpus of books? (source: Google Ngram Viewer )