Jesus made bold proclamations to the Pharisees, but the Pharisees rejected Jesus (yet again).
In response, Jesus talked about how after they lift the Son of Man up, they would know who Jesus is and does stuff based on His Father (8:28). Lifting up involves elevation, so it's possible that Jesus is referring to others not throwing Jesus down upon first glance. Giving Jesus a chance via seeing him for who He is can help us understand Jesus and his link with the Father. Additionally, as noted by Tom Constable, it's heavily implied that the lifting up can be a reference to the crucifixion, allowing Jesus to demonstrate even further His identity (Study Light).
Once again, Jesus establishes that the Father is with Jesus (8:29). Jesus meant that He and the Father connected with each other and that Jesus followed the Father.