Sorry to say but usually, some type of underlayment is used when doing this type of job because of the uneveness of a 'raw' subfloor. If you're SURE an underlayment wasn't put down first before the veneer flooring was installed, here's what I'd do.
First, I'd try using an ice chopper. That's right. Get a fine, metal file and put a nice edge on it first. BEFORE you do, go to the store and look at a NEW ice chopper to see how it 'looks'. There are right ways and wrong ways. Then, I'd take the chopper and get underneath of the wood and start 'scraping'. If you can work in parallel with the sub-floor, that's best.
If the aforementioned isn't working well, then get a circular saw and set its BLADE depth to be the thickness of the veneer flooring and start cutting perpendicular to the veneer flooring. THEN try the chopper again. The veneer may come up easier if its in smaller 'sections'.
I know I said it earlier but it troubles me that the veneer was put down right on the sub-floor. BUT, it guess someone who's not thinking can do this. Once you get the flooring off, you can hand-scrape off the 'high' spots by hand with a sander or by scraping. IF you're putting in a new floor yourself, be sure to read the warranty FIRST to be sure an underlayment isn't required. AND, be sure that whatever you end up with on the floor, underlayment and flooring included, isn't going to prevent doors from closing or give you a 'height differentail' between 2 different rooms. Just some things to consider.