The outer surface

Energy transferred to the gas is heat energy.

Explanation

Since the outer surface of the gas is rubbed and not displaced/shaken, no work will be done on the gas.

We know that,

Work done = force ×displacement

Force =pressure × area

∴work done = pressure × area × displacement

So, work will only be done when there is either displacement or the gas is expanded/compressed.

The cylinder and gas become warm because of the heat generated by friction between the polishing machine and surface of the cylinder. This heat will warm up the gas and outer surface of the cylinder.