How to look a 230V ,50 Hz AC power supply via oscilloscope from the switchboard?
It really looks like a sine wave (because it is a sine wave.)
You would do better to find a wall wart that puts out AC than to try to put something together yourself.  


An AC wallwart is nothing but a transformer.  It will lower the line voltage to something low enough for your oscilloscope to measure.

More importantly, it keeps you away from high voltages.

As a handy side effect, it prevents your oscilloscope from causing a short circuit (with associated flash, bang, and circuit breaker trip) when you accidentally connect the oscilloscope ground to the live wire of the outlet.