In short
Dil Cheez Kya Hai is from the film Umrao Jaan (1981). Sung by Asha Bhosle, music by Khayyam, lyrics by Shahryar. This is the original soundtrack recording, not a remix or a cover.
Khayyam pitched the whole score lower than Asha Bhosle normally sang, which is why she sounds like a different person here. She said it took her a long time to agree to it.
Questions
Who sang Dil Cheez Kya Hai?
Dil Cheez Kya Hai was sung by Asha Bhosle for the film Umrao Jaan (1981).
Which film is Dil Cheez Kya Hai from?
Dil Cheez Kya Hai is from Umrao Jaan (1981), with music by Khayyam.
Who wrote the lyrics of Dil Cheez Kya Hai?
The lyrics of Dil Cheez Kya Hai were written by Shahryar, set to music by Khayyam.