It's pronounced as jay-sen-see-gel.
Below are links to some YouTube videos where you can hear how Jason's name is being uttered:
https://www.youtube.com/watch?v=olKp7mkzLvw
https://www.youtube.com/watch?v=FRvnrCo4BKw&t=2s
https://www.youtube.com/watch?v=X-w7fE6eXaA
Born on January 18, 1980, Jason Segel started making movies as a teenager. He discovered acting in high school and landed his first television role at the age of 18. After two failed series, Segel scored a hit with How I Met Your Mother in 2005. He has also enjoyed success on the big screen with such films as Forgetting Sarah Marshall and The Muppets.
Segel lives in Los Angeles. He dated his former Freaks and Geeks co-star Linda Cardellini for five years.
A minister in the non-denominational Universal Life Church, Segel officiated a wedding on The Tonight Show in 2010.
Know more about the life of Jason Segel at Biography.com.
Learn How to Pronounce 25 Difficult Celebrity Names featured at Hollywood.com.