The "no-show" and "no-work" jobs are a way that the construction company pays off the mafia for getting them the contract. It's basically money laundering. Mafia buys/extorts/blackmails to get influence in the government (e.g. the assemblyman that Tony had coffee with at Italianissimo) for a public works project. They use that influence to get the contract for construction to go to a firm or union which they control or are in business with. Then they skim money off the contract, some of which goes back to the assemblyman and some of which is paid to mafia guys in the form of jobs for which they get paid even if they don't show up ("no-show") or do any work ("no-work"). Tony has a no-show "waste management" job, and Christopher used to have a no-work "investment banker" job. Almost all of the guys in the family have a "job" like this. The "jobs" give them some money, but more importantly it gives them an opportunity to file a (partially) legitimate tax return in order to keep up appearances. Somebody has a house like one of these guys and drives a glitzy car, but doesn't file a tax return - that's going to raise eyebrows eventually.
