Where in trunk? Cant find.

depends on the car. under hood, under back seat, in trunk

Did you try to pull forward the rear seats to expose the trunk?

you can try to go threw your back seat and use a big flat head screw driver to pry lockjaws open

It should be directly under the steering wheel if not its broke

There should be a positive terminal under the hood under a red cap as i am assuming ur battery is not visible, use something steel on the motor for a ground, sometimes the batteries to newer vehicles are under the rear seat so if ur having trouble finding out how to even hook up the cables i would look under the hood for the terminal first, will probly be in a random place then if u cant find that or the battery check under the back seats

Pop the hood. On the driver's side(under the hood) there is a red cap close to the hood shock. Take the red cap off and there is a metal post under it. This is used for a jump start since the battery is so hard to reach. You will want to put the positive cable(from a set of jumper cables or a battery charger) on the metal pole and the ground cable can be connected to a bolt under the hood. you may have to find a bolt that dosen't have a lot of paint under it to get a good connection. Once you can get it started again it may be easier to get the key out of the ignition. hope this helps you

You can jump your 98 528i from under your hood. On top of the center of your engine there is a positive (+) sign. You have to pry the cover open and there is also a negative ground spot to the left of that. Bmw is pretty smart!

look under the spare tire cover, should be on under side of cover, options are in alph. order. S.R. Peace

According to AutoZone.com: Front seating area, driver side, under dash, driver side of steering column

If you have the key for your vehicle, then to manually open the trunk:

[1] insert the key into the trunk key hole
[2] turn the key 45 degrees
[3] press in to manually unlock

This is important if you lose power and need to access the battery (via the trunk).