Yes, non-K processors can be overclocked.
Yes, non-K processors can be overclocked.
Is it possible to increase the processor speed to 4.4GHz or 4.2GHz?
There is a G3258 with a 1150 socket. The only unlocked Skylakes are the 6600k and the 6700k. I don't know about any overclocking for Skylake Pentiums or Celerons.
Yes, but you require a board that supports adjusting the bclk because the multiplier is fixed.
This page provides instructions for non-overclocking of the ASUS Z170 model.
there isn't a pentium anniversary feature or unlocked multiplier option. The g4400 and g4500 models don't support unlocked multipliers, so you can't use the same method to overclock them. They're considered low-end options.