I'll answer according to the jehovah's witness perspective. To the best of my knowledge, because their doctrine is updated often. This is not my perspective.
- What is your God (Jehovah) like?
- Jehovah is a kind, loving creator, fair God. He wants you to know and use his personal name, Jehovah, in order to begin a friendship with him.
- Where does your teaching come from (which writings)?
- The Bible, it's the inspired word of God. Also, Jehovah God tells the faithful and discreet slave about the true meaning of the bible. The faithful slave= the governing body of Jehovah's witness. The governing body receives correct information about Bible text from Jehovah and they share that with the congregations.
- Who is Jesus? Is he God or man or both? Did he save us from our sins?
- Jesus is a created being. Before he came to earth he was Michael the Archangel. Scripture supports the notion that Jesus is the archangel Michael. Jesus is man and A god (small g), BUT NOT Jehovah God! Jehovah God and Jesus are not equal but separate, they are not the same person. Jesus gave his life a ransom sacrifice so that we may have the chance of eternal paradise to be reconciled with Jehovah. Jesus did not save us from sin, but made it possible where we can now ask Jehovah to forgive us our sins based on the ransom sacrifice. And no animal sacrifice.
- What does it mean to have salvation?
- Again, the ransom has given us the resurrection hope. Meaning that because of Jesus' death we have a chance of living forever on a paradise earth.
- Who or what is the Holy Spirit? What is his function?
- The holy spirit is Jehovah's active force. It's not a person like Jesus but a force. A guiding force, that works in harmony with Jehovah's will. The holy spirit will even lead witnesses to knock on your door and start a. Bible study with you. That's Jehovah's holy spirit that led them to you.
- What happens after death? (both for faithful JWs and for those who don't believe)
- Only those of the 144,000 will get to go to heaven after death. But everyone else will be dead. There is no life after death, and there is no hell. The bible says the dead are conscious of nothing. Both witnesses and non witnesses are not conscious- they remain dead. But the witnesses and maybe some non witnesses live on in Jehovah's memory, until he decides to wake them up from death.
- What is sin? What can we do about it?
- Sin is doing that which is contrary to Jehovah's commands. Also, disobeying those that Jehovah has placed over you such as the governing body or the congregational elders is sinful. The governing body of Jehovah's witnesses are chosen by Jehovah to lead and not complying with instruction is as though you are saying no to Jehovah and that is sinful. What can we do about sin? Nothing, Jehovah has set a date when he will destroy those who take part in sin. Jehovah's witnesses only goal is to preach so that all may become witnesses of Jehovah and be saved from the dreadful day of Jehovah God- Armageddon.