Some of this is not a training problem, and treating it like one wastes time your dog may not have. If they are distressed when you leave, if they growl or guard their food, their toys or you, if they are frightened on the lead, or if anything about them changes suddenly at any age, contact your vet the same day. A tip from a website, ours included, is not the answer. If it cannot wait, contact your nearest emergency vet now.
With a Pug, the things that look like character are often their body. Louder sleep can be their airway. A seizure or a sudden change in behaviour can be Pug Dog Encephalitis (PDE, brain inflammation seen in Pugs). A first seizure, one that lasts more than two minutes, or more than one in a day is an emergency: contact your vet now. A squint can be an injured eye. If their breathing turns loud and they cannot settle after a walk in the heat, get them somewhere cool and contact your vet now. Bloat (GDV, a twisted stomach) needs the same speed: a swollen, tight belly, retching with nothing coming up, sudden restlessness or drooling. It can happen in any dog, though it is most common in large, deep-chested breeds.
They'll keep grumbling about the sofa. If the grumble turns into a fight for breath, contact your vet now.