I want to put a slab of wood on top of my .5" x 39.5" long x 21.75" wide x 13.75" high tempered glass coffee table. Will it hold it?
According to hunker.com, a piece of 1/4" tempered glass, supported every 12 inches can support 292 pounds per square foot. The same web site suggests that 3/4" tempered glass supported every 12 inches can manage 3268 pounds per square foot. This implies a non-linear increase in strength based on thickness. Being very conservative, one might simply double the 1/4" thickness figure and round it to about 600 pounds per square foot, if supported every 12 inches.
Your table is approximately 6 square feet in area. This implies that one could apply 3600 pounds to the surface of the table if it was supported every 12 inches. It is not.
It's unlikely that your slab of undefined wood of undefined dimensions is going to weigh 3600 pounds.
If your slab of wood is going to match the size of the top, placing the weight uniformly over the table, it will be well enough distributed. Such distribution will also place the forces on the vertical legs of the table.
I think it's safe to say that you could have two hundred pounds of wood on this table and not fear to break it. One should not apply side forces to the table when moving. Remove the slab if you have to slide the table unless otherwise managed. I'd be willing to go as high as four hundred pounds if the table is never going to be moved, but what kind of wood slab is going to weigh four hundred pounds?
These figures are conservative, which means I might be on the safe side by many orders of magnitude.