Where is model number located on ibm thinkpad laptop?

Turn your ThinkPad over, look on the bottom. There should be a sticker that has M/T and S/N on it. The "M/T" is your specific ThinkPad Model and Type. You need to know both the Model and the Type ... since many ThinkPad "models" have a dozen or so different "types" within that model family.

If there is no sticker on the bottom of the laptop chassis, or it was worn off, you can alway press F1 and bootup and go into the laptop's BiOS setup. The first screen of the BiOS setup will tell you the Model and Type.