A human with the ability to control electricity with their mind (electrokinesis I think?) would need electricity to manipulate I'm assuming. So if they were caught off guard without any available electricity or a power source to manipulate, could they generate their own? For example: could they generate static electricity from rubbing their hair on their head or arms? And would it be possible to make enough electricity to use to power things or to use in combat?
This is a Frame Challenge
I believe you're looking at this the wrong way. Remember, the goal isn't to be scientifically precise but to achieve suspension of disbelief. After all, we're dealing with a superhero, right? So think of it this way: The human body has no need to generate electricity — the world is swimming in electricity. Literally every atom in the entire universe has electrons in orbit. They come out of that orbit and move around due to electromagnetic forces or energy.
You see, electricity is the movement of electrons, but electrons move in accordance with the rules of electromagnetic energy. For example, if you move a magnetic field past a wire, the motion of that field stimulates the movement of electrons in that wire.
Why is this important?
Because the Earth's magnetosphere, the motion of air, the shift of ground charges, etc., provide a veritable soup of electrons floating around all around all the time. It's why lightning exists.
And if that weren't enough, humanity is generously pumping a breathtaking amount of EM energy into the biosphere.
Your superhero needn't draw a single electron from his/her own body. There's so much electricity in the world that it's a wonder we don't all walk around with our hair sticking up. But as a result, there are some cool side effects that you can take advantage of.
If your superhero is near power lines, the houses and commercial buildings brown- or black-out until he/she's done doing the voodoo they do.
Or if your superhero is near a cell tower, the phones drop out.
Or if your superhero is near combat... or in a mine or similar... radios stop working.
Or if you want to be a bit less dramatic (sometimes less is more!) then when your superhero is strutting majestically down the street (which superheros do, dontchaknow), the neon and LED lights along the street flicker with his/her passing. Cars dim-out and stutter until they've passed. Etc.
I think you can have a lot more fun with this if you don't worry about how the body can generate electricity and worry more about the sources of electricity that are already around you — literally everywhere.
A dynamo or battery
Think back to anything you've done and uf it generated electric shocks. Likely you've had static discharge during your life, especially socks and carpet. At worst the shock might've put the most minor of burns on a nail or something. It's a nasty shock, but in combat with adrenaline you're unlikely to notice it as nasty at all. It is also not enough to power anything, so it's quite useless. Attacking open electronics is your best bet and even then very unreliable.
To improve electricity generation, get a hand cranked dynamo. I can only find some ok statistics about cycling and generating power, which is 100 watt for an average person cycling normally. Leg muscles are much stronger than arms and the 'circle' movement is much more natual for the legs, so I'm assuming 25 watt for hand cranking.
My research about tasers shows that the modern tasers have about 26 watts of power. Older models about 7 watts. With around 50000 volt and a low ampere you should be able to replicate these results. The dynamo must be able to crank that exact configuration or the electrokinetic should be able to adapt is on the fly. Tasers can definitely be lethal in different configurations.
This does give rise to the question why not batteries. They can hold a ton of potential power. They can give this as electricity gradually or with the right short-circuit you can get this in big bursts.
As your question seems to indicate no such things are available I would say you're out of luck. The best thing I can imagine is to impart some electrical impulses in the opponents nervous system or even high jack it all. You might not have the fine control of electricity to control his or her body, but certainly enough to disrupt them. Not just changing the impulses in the spine and brain for seizure like effects, but imagine changing the impulses at the big knot of nerves at the heart. A heart failure is then easy enough.
Human body generates a lot of electricity... over time. Not in an instant, though.
For electrokinesis I see two options:
without any external source - make it that the person you want to can use it very precisely. Then a tiny electric charge form his body is shot towards the target, incapacitating it. Overload optical nerves, for example, to cause momentary blindness, or paralyze for a moment attacking Cerebellum, or disorient or disrupt bodily functions by concentrating on pons.
with external source - if someone is electrokinesis-capable, it would be great idea to take some sort of a capacitor everywhere and store some electricity in it. Lot of small ones, looking like jewellery or few big ones in a backpack. Capacitors can be built using crudest of tech (for example, allegedly, Ark of the Covenant, if built according to description in the Bible, is a rather big and nasty capacitor).