Since He has been falsely accused He has requested and given honest hearted humans the privilege to testify on His behalf. Jehovah has been accused by Satan and his followers of not ruling in a just manner (Gen. 3:4,5; Jn.8:44).
We witness to the fact that Jehovah has not caused the terrible things that adversely affect humankind, but it is humans themselves who cause their misery because they have rejected God's rulership and counsel (De.32:5; Js. 1:14).
We have also witnessed Jehovah's love and guidance for righteous humans and His warning to all humans to change their incorrect life course while they can.
We also have seen the evidence of True Christianity such as love within the organization known as Jehovah's Witnesses.
We also witness to the fact that most religions cannot meet this requirement. In fact, when you examine most religions you find that they cannot meet any of the requirements of true Christianity. Their historical record is of bloodthirsty wars, immorality, sectarian violence and factional splits (Mat.7:21- 23; 2Tim. 3:5; Gal.5:19-23). Today Catholics continue to kill Catholics, Protestants kill Protestants, and Mormons kill Mormons, something true Christians would not do (1Jn.3:10,15; 4:8).
We also are witnesses to the fact that Jehovah's Witnesses demonstrate that they have the Holy Spirit because its adherents have the power to live according to Christian standards.
And we again have witnessed that other religions do not give evidence of having Holy Spirit, since they cannot get their congregation members to live moral lives. They allow practicers of homosexuality, fornication, or adultery to be accepted members of their congregation (Gal.5:22ff; 1Cor.6:9; cf. Gal.5:19ff; 2Tim.3:5). They turn a blind eye to such sins and so their "fruitage" is not a spiritually clean congregation, free of non-Christian lifestyles (1Cor.5:11-13).
We also witness the unity within the true Christian congregation of Jehovah's Witnesses while other religions cannot even agree on abortion, homosexuality, special gifts, or baptism (1Cor.1:10, 2 Cor.13:11, Phil.1:27).
We are also witnesses of the fact that Jehovah's Witnesses right now are performing the greatest Bible education work in all human history! (Matthew 24:14, 28:19, 20).
The above is the chosen best answer to this question by Bar_Anerges.
"What Have Jehovah's Witnesses Witnessed?" - How Did Jehovah's Witnesses Get Their Name? (Defend Jehovah's Witnesses)