Smirk does not have a suffix. Usually words with only one syllable, don't have a suffix.
The suffix "-y" can be added to "smirk" to create the word "smirky." This suffix is used to describe someone who often wears a smirk on their face.
The prefix of the word "smirk" is "sm-" which means a slight curling of the lip, often indicating amusement or smugness.
The suffix word of "constitutional" is "tion," which forms the word "constitution."
The suffix of the word "magician" is -ian.
The suffix of the word "customary" is "-ary."
The suffix in the word duties is -ies. This suffix just makes words plural.
The word smirk is a noun meaning sly smile. Synonyms for the word smirk include beam, grin, leer, simper, grimace, grim, sneer, visage, and smug look.
smirk
Grin.
Josh had a smirk on his face when he got a B+ on his test.
Grin or smirk
smirk
perhaps "grimace"
smilestilestalestarestarksharkshirksmirk
"Johnny had a mischievous smirk upon his face after having read his sister's diary."
Smiling, beaming
quirk, smirk, shirk
Smirk is one alternative.