I want to place an adsense banner on my wordpress theme, http://submityoursandwich.com/ right under the top navigation bar in the white space. above all the posts which file or where should i look to place the code
I think you can utilize more than one banners in this theme as the theme is very useful for adsense. You can definitely place a slow just below the menu bar, adsense link units may work better there. You can try editing the header.php file in your theme. You can also insert adsense units in-between your posts and also at the end of single posts which can be done by editing the single.php file.