my question might be sillier than it seems....

i'm starting from Gaussmarkov layout (and website), in his description, Gaussmarkov says "Choose values for the three 100K resistors that give you JFET drain voltages of 4.5V to 5V", my question is: where do I have to measure the drain voltage of each JFET? I don't know in which part of the circuit place the VOM probe to measure said voltage
PS: i apologize for my ignorance!!!!!!