What is the ruling on working secretly (working in the black market) and what is the ruling on unemployment benefits received while job opportunities are available and rejected in a country that prohibits such actions?

If a Muslim enters a country under a covenant, he must abide by its laws as long as they do not violate the Sharia. If working "under the table" means tax evasion, it is not permissible if taxes are in exchange for services. However, if taxes are levied without any services in return, then it is an injustice, and it is permissible to evade them through undeclared work. And if the country's laws stipulate not working to receive unemployment benefits, then it is not permissible to violate them.