Acento is an Uncountable noun?

Hola Shirley

Not really - the reason to drop the article is because there are some set expressions in Spanish that don't use any article as in treating that "object" , in this case "acento", as something very general. "Coger acento" is something we say often as an expression, the same way as other expressions like: tener coche (to own a car), tener trabajo (to have a job) or for example pedir cita (to book an appointment). 

All these are seeing more as prototypical/generic and tend to omit the article.

I hope it helps.

Saludos