Thank you all for your replies. The shirt is for a child and is almost like a long underwear fabric. It was very popular at Target this year for toddler boys long sleeve shirts. I think I will skip trying to embroider on it.
So, it is like a thermal henley type T-Shirt? If yes, I have done some. I use a mesh stabilizer and WSS topper...make sure you are not using any thin fonts as they tend to sink into the weave...I then use Pellon Knit Iron-On Interfacing over the back of the embroidery to keep it from scratching the tender chest skin...make sure you use lots of steam if you apply this...
I have several yards of this fabric but never tried to embroider on it. I have made a few wearable items with the waffle fabric. I may try embroidering on a scrap piece. I think I would use a medium cutaway stabilizer and not dense design also use WSS on top.
Knock down stitch first? Never even seen a waffle weave t-shirt
Considered it and thought better. Maybe an applique or a patch would work if you just must! Let us know YOUR tricks if successful.