If the only existing finish is truly wax, then white spirits and scrubbing along the grain with either 0000 steel wool or a red or green nylon abrasive pad should remove it. Lots of white spirits and repeated scrubbing is needed. If, after this and a little light sanding (180 - 240 grit), again with the grain, you're still not absolutely sure you've removed all the wax, you could use a barrier coat of dewaxed shellac between the suspect wood and the lacquer. The mention of dewaxed shellac is important: shellac is very good at coping with contaminants, and it provides a good base for a lacquer such as pre-cat or acid cat lacquer. If you are unable to completely shift the wax, and you go straight to a lacquer you're very likely to experience poor or failure to adhere, possibly including in crawling of the finish away from a waxy spot. Slainte.