With regard to Charles Taze Russell, the founder of the Bible Students in Allegheny, Pennsylvavia, U.S.A., the April 2000 Watchtower Study Edition, How Does God’s Spirit Operate Today? had this to say about the founder of the Bible Students (who preceded the organisation now known as Jehovah’s Witnesses):
One member of this group, Charles Taze Russell, said regarding his quest for Scriptural truth: “I prayed . . . that I might be enabled to rid my heart and mind of any prejudice that might stand in the way and be led of his spirit into the proper understanding.” God blessed this humble prayer... Through the pages of Zion’s Watch Tower and Herald of Christ’s Presence, Russell and his associates courageously denounced false religious doctrines that misrepresented God.
“Our Lord’s assurance,” said Russell, “is that . . . the holy spirit of the Father, sent on account of and at the instance of Jesus our Redeemer, Mediator and Head, will be our instructor.” And instruct it did! These sincere Bible Students continued to take in the pure waters of truth from the Bible and proclaim them worldwide.... Holy spirit may not remove trials or temptations; it can, however, help you to endure them. By relying on God’s spirit, we can receive “power beyond what is normal” to deal with any trouble or distress.—2 Corinthians 4:7; 1 Corinthians 10:13. Source: https://www.jw.org/en/library/magazines/w20000401/How-Does-Gods-Spirit-Operate-Today/
The above is a somewhat non-specific testimony which says nothing about any dramatic or spectacular experiences. The rest of the article is somewhat vague, although a 1962 Watchtower article had this to say about the experiences of several Jehovah’s Witnesses:
A GUATEMALAN full-time minister of Jehovah, after a trip by bus, walked twenty-five miles to get to his ministerial assignment. This he accomplished even though the road was rocky and led over mountains and he was burdened down by a seventy-pound suitcase. Another like minister in Southern Rhodesia, after going as far as the bus would take him, walked a hundred miles in five days to get to his territory. A Christian witness in Russia was brought before a community court because of her preaching Bible truth. In spite of many threats and jeers by the court and other onlookers she remained firm and calm, saying to her opposers: “I am dedicated to serve the God who rules the universe, and I will never desert him under any conditions.” A Hawaiian minister, eighty-four years old and severely bent, devotes 150 hours monthly to the public ministry. What enables all these to perform such things in order to preach the Kingdom message? Activation by Jehovah’s spirit.—2 Cor. 4:7; Phil. 4:13.
The foregoing are but a few of the many incidents reported in the 1962 Yearbook of Jehovah’s Witnesses. It gives eloquent testimony to the fact that the Witnesses are activated by Jehovah’s spirit, that they are indeed “aglow with the spirit.”—Rom. 12:11.*
What does it take to receive this dynamic force of Jehovah, this holy spirit of God? ...for one to receive holy spirit he must also be in touch with God’s channel of communication. Just as in the days of Jesus and the apostles receiving of holy spirit was dependent upon contact with God’s channel of communication, his earthly representatives, so also today. The facts show that that channel is found with the New World society of Jehovah’s witnesses.—Acts 19:1-7. Source: https://wol.jw.org/en/wol/d/r1/lp-e/1962247?q=testimonies+holy+spirit&p=doc
I searched in vain for any individual testimonies from Jehovah’s Witnesses who might have had a life-changing encounter with ‘holy spirit’. Perhaps that is because they believe what Trinitarian Christians respectfully call Holy Spirit is, to them, simply Jehovah’s impersonal source of power or ‘active force’ – an ‘it’. That’s why they do not capitalise the words holy or spirit.
One thing that became clear as I searched their web site is that individual testimonies are always down-played and attention is always focused on the organisation. The men who head up the organisation belong to the "remnant of the 144,000" class, those who believe they are anointed, spirit-filled Christians with a heavenly hope. Indeed there are only about 20,000 anointed Jehovah’s Witnesses throughout the world. The rest, the majority, have been told they can only have a portion of this spirit because they are not part of the 144,000 anointed class.