In its comment on John 6:20, the second edition of the The Ignatius Catholic Study Bible reads:
The Ignatius Catholic Study Bible - John 6:20
It is I: Or 'I am'. The reassurance that Jesus gives to the disciples is also an act of self-revelation. His words recall the holy name 'I am' that Yahweh revealed to Moses at the burning bush (Ex 3:14). The claim to divinity inherent in this name is substantiated by Jesus' exhibition of power over the laws of nature (6:19; Job 9:8). Several times Jesus claims this divine name for himself in the Fourth Gospel (8:24, 58; 13:19; 18:6) (CCC 213).
do not be afraid: Words often spoken when God reveals himself to his people, whether directly or through an angel (Gen 26:24; Judg 6:22-23; Lk 1:30).
Above, the Ignatius Commentary states that Jesus, in John 6:19-20, was identifying Himself as the "I Am" of Exodus 3:14, based on His usage of egō eimi (ἐγώ εἰμι) ("I am", "I am he", "I am the one"). This argument is commonly given in Trinitarian apologetics for the passages John 8:24, 8:28, 8:58, 13:19, 18:4-6, but not often for this passage.
The passage says:
John 6:19-20
19 So when they had rowed about five and twenty or thirty furlongs, they see Jesus walking on the sea, and drawing nigh unto the ship: and they were afraid.
20 But he saith unto them, It is I; be not afraid.
The Ignatius Study Bible interprets Jesus's words here as an intentional claim to be Yahweh. But, this is a severe over-reading. Jesus is simply identifying Himself to His disciples, and the parallel passage of this incident given in Matthew reveals what His disciples thought of His identity, namely, that He is the "Son of God":
Matthew 14:32-33
32 And when they were come into the ship, the wind ceased.
33 Then they that were in the ship came and worshipped him, saying, Of a truth thou art the Son of God.
If one believes that Jesus is God, that would be what they would confess here. A "son of" someone is in every normal circumstance not that person, and there is no indication that by "Son of God" the disciples meant "God", "God the Son", etc.
In most instances where Jesus uses the term egō eimi in the Gospel of John, He is identifying Himself as the Messiah (see John 4:25-26). Here (and in Matthew 14:27, Mark 6:50), however, He is probably just using it as a term of self-identification, essentially to say, "It is me, Jesus", similarly to how the formerly-blind man uses it in John 9:9 ("I am he", egō eimi).
In summary, Jesus is not identifying Himself as the "I Am" of Exodus 3:14 in this passage, or the others in the Gospel of John where He says egō eimi. He usually uses it to claim to be the Messiah, though in this context, He is probably just using it to self-identify.