Usually after “short” vowels in words of more than one syllable.

egg

Hogg

aggressive

aggrieve

aggro

bagging

befogged

beggar

begging

bewigged

bigger

boggling

braggart

bragging

bugging

chugging

clogging

dagger

debugged

digger

digging

dragging

drugging

earwigged

eggplant

eggshell

flagging

flogging

giggle

haggard

haggis

hogget

hugger

hugging

jogger

jogging

juggle

laggard

lagging

leggings

logging

lugger

lugging

maggot

mugging

nagging

niggle

noggin

nuggets

pegging

plugger

plugging

priggish

quagga

ragging

rigging

ringgit

sagging

shrugging

slagging

slogging

slugging

sluggish

smuggest

smuggle

snigger

snuggling

stagger

swagger

swigging

thuggish

toggle

unclogged

wagging

waggish

wiggle

zigzagged