1. Can one be saved without it? No, The Holy Spirit teaches, baptizes (washes) and seals. without the HS there is no salvation.
2. Must the church have it? Yes, for without him, the churhc is no church at all
and which church? The true church, all who place their faith in Christ. What denomination? All who teach the one true gospel of Christ.
3. Once you have it how do you know you're got it? You will be chastened when you fall into sin. Things which did not make sense before in scripture now are made clear. Many things can show us we Have Gods spirit. One this is Hope. For without hope, we have no life. because we have no faith.