Whenever John described Jesus as crying out, an important public pronouncement followed (cf. John 1:15; John 7:37; John 12:44). Jesus said that His hearers did know Him. Probably He meant that they knew who He was superficially (cf. John 7:24) and knew that He had an earthly origin ( John 6:42), but they knew less than they thought. Jesus was speaking ironically. They did not know the One who had sent Him, though Jesus did because He had come from that One. [source][source][source]
The One who had sent Jesus was true (Gr. alethinos, real). Jesus meant that God really had sent Him regardless of what others might think about His origins. Unfortunately they did not know the One who had sent Him even though they prided themselves on knowing the true God (cf. Romans 2:17-19). They did not know God because they did not know their Scriptures (cf. John 5:46). They did not know Jesus because they did not know the Father who had sent Him. In John 7:16 Jesus disclaimed originality for his teaching, and here he disclaimed responsibility for his mission. [1][source]
"He was once again claiming to be God! He was not simply born into this world like any other human; He was sent to earth by the Father. This means that He existed before He was born on the earth." [2][source]