Always use only licensed electricians and always have them pull a permit, please.
Knob and tube is an outdated system of wiring that was installed until the 1940’s. It is a system of separate single hot and neutral conductors with no ground. Because of the porcelain insulating components, if undisturbed, and not overpowered with modern appliances, knob and tube wiring will last indefinitely. Unfortunately, in today’s world there are many situations where knob and tube is not acceptable.
For one thing, many insurance companies will not cover a house that has knob and tube. When buying house, it may be necessary to remove the knob and tube within 60 days after closing to get insurance. Knob and tube must be removed from the attic before insulation can be installed. This is because the wires may overheat without free air circulation around them.
When it comes time to add insulation in walls or attic, the knob and tube must be removed from that area. This is because the wires may overheat if they do not have free air circulation around them as was originally intended.
Knob in tube can last a very long time if it is unaltered, undisturbed, and not overloaded. Even adding new receptacles and ceiling light fixtures adds to the risk because the wiring is disturbed. Having a new looking 3 prong receptacle that is not grounded increases the chance of overload and accident. Certainly, major renovations to the house are reason to remove all knob and tube wiring that is exposed.
Knob and tube gets less and less safe as more changes and modernizations are made to the house. In the writer’s humble opinion, in the near future knob and tube will be uninsurable, and therefore useless.
Any licensed electrician will tell you to get rid of your knob and tube wiring. There is plenty of information online if you want to immerse yourself in the subject.
Find out if your house has knob and tube wiring. If you are not sure, ask a licensed electrician to remove a device or two and look for it. It is important to know! Take a time out and wiki knob and tube, or google it.