口 is the mouth radical and signals onomatopoeia, sound coming out of a mouth. Chinese routinely uses 口 + a phonetic to coin imitative sounds, like 嗡 buzz, 嘀 tick, 嘶 hiss. Here it frames the sizzling-fat or hissing-pan effect.
兹 gives the sound zī directly, same tone. The classical 'this/herein' meaning has no role, pure phonetic borrowing to spell a hiss-like noise. 兹 here is slightly contracted to fit alongside 口 on the right.
No stroke data for 嗞; the glyph shown is your device font, so component strokes can't be highlighted.
