No show job
 

I think in Spanish it's sinecura. Is this the common term?

It's not common at all (not in Mexico, at least). Here, the colloquial term is "(trabajo de) aviador", and the most commonly used in the press as well. It is compared to someone who lands in a plane, takes the money and lifts up again.

In some semi-official documents I have seen "personal fantasma" or the whole definition as "personal que cobra sin presentarse a trabajar".

In Spain, colloquially, one talks about "un chollo" (like "a plum job in the foreign service" or the like...)

Tiene un chollo en la Oficina de Correos...