w08 2/15 23-24 'Christ's presence what does it mean to you?' says:
The time period during which “this generation” lives seems to correspond to the period covered by the first vision in the book of Revelation. (Rev. 1:10–3:22) This feature of the Lord’s day extends from 1914 until the last of the faithful anointed ones dies and is resurrected.—See Revelation—Its Grand Climax At Hand! page 24, paragraph 4.
w10 4/15 10-11 'Holy Spirit's role in the outworking of Jehovah's purpose' says:
14 What does this explanation mean to us? Although we cannot measure the exact length of “this generation,” we do well to keep in mind several things about the word “generation”: It usually refers to people of varying ages whose lives overlap during a particular time period; it is not excessively long; and it has an end. (Ex. 1:6) How, then, are we to understand Jesus’ words about “this generation”? He evidently meant that the lives of the anointed who were on hand when the sign began to become evident in 1914 would overlap with the lives of other anointed ones who would see the start of the great tribulation. That generation had a beginning, and it surely will have an end. The fulfillment of the various features of the sign clearly indicate that the tribulation must be near.
On the jw.org online library these are found under Generation: 'understanding clarified (2008)'. Right under 'understanding clarified (1995)'