What is Gift of Holy Spirit?
Special endowment from Holy Spirit given to those bearing testimony of the Savior Jesus Christ the only begotten of God

Will Gift of Holy Spirit cease?
It will not. However some gifts of Holy Spirit may not be used all the times e.g. tongues speaking

Will the one speaks in tongues know what he is speaking?
Yes, because it is gift works for him just like prophetic gift works for prophet.
If one who speaks in tongues will be out of control of the tongues he is most probably controlled by the evil spirit because only evil spirit tend to work by controlling

Will the Gift of Holy Spirit be given only after baptism ?
It is a endowment to the one with faith in Jesus Christ, not for baptism, but of course the one with faith will surely receive baptism. In Act 10 we learn the story of Cornelius and his household, they had gift of Holy Spirit poured on them before baptism. One important point is that gift of Holy Spirit will not always follow one who do not have faith and baptism but always follow one with faith and baptized.