Normaly when you are on dialysis, the electrolytes are checked on your monthly lab draw. If for some reason the results are off, they may check more often. It can also depend on many things such as:
Change in your illness and type of illness you have
Changes in medication
If you are having any issues that require attention
They can be drawn at clinic, in the lab or even at home if you are on hemo dialysis. I have never heard of anyone coming to the house to draw labs.
You should discuss this with your Doctor. They should be able to answer for you.