JOHN 19:28 Jesus knowing that all things were now accomplished, that the scripture might be fulfilled said “I THIRST”
Let us break this verse into parts and meditate on it:-
Knowing
Jesus knows all things. He is the Alpha & the Omega. He is part of our creation, so he knows all things.
John 2:24 Jesus …knew all men, 25 and had no need that anyone should testify of man, for He knew what was in man
Heb 4:12 For the word of God is living and powerful, and sharper than any two-edged sword, piercing even to the division of soul and spirit, and of joints and marrow, and is a discerner of the thoughts and intents of the heart.
John 1:1 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 18:4 Jesus therefore, knowing all things that would come upon Him, went forward and said to them, “Whom are you seeking?”

Scriptures/All things were accomplished:-
From early times, the Scriptures have been talking about the sacrifice of a lamb. In Exodus it talks about a lamb of the first year, without blemish and bones not broken. It also prophecies about the crucification of Christ and the events that happened at the cross.
Exo 12:46 nor shall you break one of its bones
Ps 22:1 Why have you forsaken Me
Ps 22:16 Hands & Legs Pierced
Ps 22:18 They cast lots at the cross
Ps 50:18 When you saw a thief, you consented with him
Psalms 69:21 They gave me gall for food; for my thirst they gave me vinegar to drink

Which Thirst?
Thus Jesus knew all the scriptures and tried to fullfill them. He then said He was thirsty. Thirst could refer to Physical thirst and Spiritual Thirst. Why would Jesus have to thirst for water. He controlled that water both Physical and Spiritual. In John (3:3 and later), Jesus referes to Spiritual water when he talks about water in all the references.
Physical
John 2 Jesus changed water to wine
Matt 8:25 Jesus commands even the winds and water, and they obey Him!
Matt 14:25 Jesus walked on the sea.
John 21:1-6/Luke 5 Jesus controlled the fish into the net.
Spiritual
John 4:10 ...He would give living water. 14 whoever drinks of the water that I shall give him will never thirst. it will become in him a fountain of water springing up into everlasting life. 6:35 he who believes in Me shall never thirst.
John 7:37 “If anyone thirsts, let him come to Me and drink. 38 He who believes in Me, out of his heart will flow rivers of living water. ” 39 He spoke concerning the Spirit, whom those believing in Him would receive
Rev 21:6b I will give of the fountain of the water of life freely to him who thirsts.
22:17 “Come!” And let him who thirsts come. Whoever desires, let him take the water of life freely. Is 55:1 Everyone who thirsts, Come to the waters

We see that Jesus also had control over spiritual water. I believe he was thirsty but more of a Spiritual thirst for souls and our Salvation. Are we ready to partake in His suffering and thirst, if we do not thirst for righteousness, we may end up with a different thirst like the rich man in Luke 16:24.
Matt 5:6 Blessed are those who hunger and thirst for righteousness, For they shall be filled.
Luke 16:24 Rich Man: have mercy on me, send Lazarus with water and cool my tongue; for I am tormented in this flame.

Why did Jesus have to thirst?
We were the ones who should have suffered that thirst. But since we did not thirst for righteousness, he took over our iniquities and thirst, that we maybe saved.
Matt 11:28 Come to Me, all you who labor and are heavy laden, and I will give you rest. 29 Take My yoke upon you and learn from Me, for I am gentle and lowly in heart, and you will find rest for your souls. 30 For My yoke is easy and My burden is light.”
Isa 53:5 But He was wounded for our transgressions,
He was bruised for our iniquities;
The chastisement for our peace was upon Him,
And by His stripes we are healed.
6 All we like sheep have gone astray;
We have turned, every one, to his own way;
And the LORD has laid on Him the iniquity of us all.

Would we quench His thirst?
Jesus explicitly said he will separate the goats from the sheep in a parable since they did not quench His thirst. But still none of His disciples quenched His thirst at the cross. He even asked to give our enemies water, but we ended up treating Him worse than one.
Mat 25:33 the Son of Man will separate sheep on His right hand, but the goats on the left. 35 I was thirsty and you gave Me drink; 42 I was thirsty and you gave Me no drink; 45 inasmuch as you did not do it to one of the least of these, you did not do it to Me.’ Rom 12:20 Enemy thirst; give him drink
If you were there at the Cross would you have quenched His thirst? It is not too late. Jesus us alive and still thirsty for our souls. Today, you have a choice to quench his thirst, with your soul. Give your life to Jesus and quench His Thirst that your thirst will also be filled with Everlasting and Living Waters.