This is what I've found so far:
Noun Hindi: मुस्कान f (muskān) Russian: усме́шка (ru) f (usméška)
Verb Indo-Iranian: *smáyati Proto-Slavic: smьjati (*smijàti)
PIE: *(s)meyh₂-
English: Smile
This is what I've found so far:
Noun Hindi: मुस्कान f (muskān) Russian: усме́шка (ru) f (usméška)
Verb Indo-Iranian: *smáyati Proto-Slavic: smьjati (*smijàti)
PIE: *(s)meyh₂-
English: Smile
The answer is no. Hindi muskān cannot derive from the Sanskrit root SMI; the vowels do not match. Turner derives it from a hypothetical ancestor *muss.
https://dsalsrv04.uchicago.edu/cgi-bin/app/soas_query.py?qs=muss&searchhws=yes
You seem to have answered your own question! To our current understanding, yes, they are cognates, also cognate with English "smile", "smirk", and (less directly, via Latin via French) "admire" and "miracle".
This PIE root is quite well-attested, and has direct descendants in many different Indo-European languages. I don't know enough about Hindi to talk about the derivation there, but in Russian, -шка is a productive noun-deriving suffix.