investigation vs questioning

investigation

noun
  • The act of investigating; the process of inquiring into or following up; research, especially patient or thorough inquiry or examination 

questioning

noun
  • The action of asking questions; a survey; an inquiry. 

  • Interrogation. 

  • The act of challenging, wondering, and doubting. 

adj
  • Unsure of one's sexual orientation and/or gender identity. 

  • Characterized by questions, inquisitiveness, doubt, or wonder. 

How often have the words investigation and questioning occurred in a corpus of books? (source: Google Ngram Viewer )