Please show me from the Gospels alone the Trinity.
Certainly.
Now the actual passage in question before you arrived was Matthew 28:19* Therefore go and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit*
The idea that God would equate Himself with a lesser being (be it Jesus) and have Baptism done in God’s name and something lesser than God would never be accepted by a Muslim. Nonetheless Jesus also commands the disciples to, “go out into all nations” and do such. So here either Jesus is blaspheming by putting Himself on the same level with God, as well as the Holy Spirit (if He is not God as well) or Jesus is making Himself equal with God.
This ties in well with John’s Gospel as he sets the stage in how the entire Gospel ought to be read:
1 In the beginning was the Word, and the Word was with God, and the Word was God. 2 He was in the beginning with God. 3 All things were made through Him, and without Him nothing was made that was made.
John is stating that not only was the Word (Jesus) with God, but the Word was also God at the exact same time. The belief that not only Jesus was God and with God is found at the beginning of John and is believed by both you and I. We believe that Jesus was fully God, and with God at the same time and we also believe the following passage
14 And the Word became flesh and dwelt among us, and we beheld His glory, the glory as of the only begotten of the Father, full of grace and truth. This is in direct contradiction of, “Allah begetteth not.”
After John sets the stage he continues to explain the context of his Gospel: *5:18Therefore the Jews sought all the more to kill Him, because He not only broke the Sabbath, but also said that God was His Father, making Himself equal with God. *
This also works hand in hand here: *Mark 14:61But Jesus remained silent and gave no answer. Again the high priest asked him, "Are you the Messiah, the Son of the Blessed One?“62"I am,” said Jesus. “And you will see the Son of Man sitting at the right hand of the Mighty One and coming on the clouds of heaven.63"The high priest tore his clothes. “Why do we need any more witnesses?” he asked.64"You have heard the blasphemy. What do you think?” They all condemned him as worthy of death.
*
A High Priest would have known exactly what Jesus was saying here, and he was so angry that he even tore his clothes and accused Jesus of blasphemy. High Priests were very well versed in their Theology and would have had no reason to over-react if Jesus was not saying what is obvious.
Also, for further evidence from Mark (because Muslims rather like Mark.) we have the entirety of the Trinity found in 1:10 And immediately, coming up from the water, He saw the heavens parting and the Spirit descending upon Him like a dove. 11 Then a voice came from heaven, “You are My beloved Son, in whom I am well pleased.”
The idea that God would call Jesus His Son is foreign to Islam but is found all throughout Scripture. Let’s take a look at the Transfiguration:
Matthew 17:1After six days Jesus took with him Peter, James and John the brother of James, and led them up a
high mountain by themselves.2There he was transfigured before them. His face shone like the sun, and his clothes became as white as the light… 5While he was still speaking, a bright cloud covered them, and a voice from the cloud said, **“This is my Son, whom I love; with him I am well pleased. **Listen to him!”
Mark 9:2 Now after six days Jesus took Peter, James, and John, and led them up on a
high mountain apart by themselves; and He was transfigured before them…7 And a cloud came and overshadowed them; and a voice came out of the cloud, saying, “**This is My beloved Son. **Hear Him!”
Luke 9:28 Now it came to pass, about eight days after these sayings, that He took Peter, John, and James and went up on
the mountain to pray…35 And a voice came out of the cloud, saying, “
This is My beloved Son. Hear Him!”
Not only is it found in Matthew, Mark and Luke but Peter even relates this story:
2 Peter 1:16 For we did not follow cunningly devised fables when we made known to you the power and coming of our Lord Jesus Christ, but were eyewitnesses of His majesty. 17 For He received from God the Father honor and glory when such a voice came to Him from the Excellent Glory:
“This is My beloved Son, in whom I am well pleased.” 18 And we heard this voice which came from heaven when we were with Him on the** holy mountain.**
There’s much more than this, and I know the Church is important to you and I’m not arguing that, but I feel like you didn’t need to say what you said for this specific conversation. Hope we’re still friends!

Merry Christmas!