The Student of the Year star was an assistant director on Karan Johar's My Name Is Khan, in which Khan played an autistic character.
Speaking to IANS, the 24-year-old debutant said: "During that film, his script used to be scribbled with notes. I used to take the scripts to him and asked him what it is. It was all his references, his homework. So we could just learn by looking at him.
"He is an institution of acting, the way he functions, the way he goes about his work, you could just learn by looking at him."
Dhawan's co-star Siddharth Malhotra also received guidance from Khan when he worked as a clap boy for My Name Is Khan.
"During the shooting of My Name Is Khan, he [Khan] came to know that we both wanted to act. I used to give the clap and then sit down," explained Malhotra.
"He used to prepare his lines and then suddenly he used to start talking, 'You should come early, see the props, touch things and feel them, look at your surroundings'.
"Initially I did not understand who he was talking to and then I used to look up and realised that Sir is telling me. Then a lot of times after the shooting he used to tell me and Varun how the scene came out or how to use actions and props."
Khan is the co-producer of Student of the Year and reportedly makes a special appearance for the song 'Vele'.
Said to be inspired by Glee, the film also stars Alia Bhatt and marks the debut performances of the three star leads.
Student of The Year releases on October 19.