How much MHz should my 1050Ti use while on battery power? PS I have Lenovo legion y520?

MHz is a clock frequency and on battery, almost always the system uses graphics in the CPU. You'll have a hard enough time forcing a GTX 1050 TI Mobility to work at all on battery and hard to know how long it will run on battery power.
What are you asking about the GPU clock?

Most likely 0 MHz, as it will be disabled and all GPU activity will go through the CPU's embedded GPU, while on battery.