adding another table to product.tpl

[madmega]

Hi, i've searched for this for a long time, and i do not exactly understand how to do it.
I have the file products.tpl

In there i want to add the following line

{$category_product->id_product|@debug_print_var}

But it results in NULL

I call it a table, but maybe i have the wrong name for it.

I cannot call to the table ps_category_product and row id_product, inside product.tpl, i do not understand why, can somebody assist me ?