I drink a shake which is supposed to contain 20 grams of whey protein per scoop, but I double up the scoops to  make 40 grams per shake. Am I wasting powder, or can my body absorb/metabolize 40 grams in 1 sitting? Can I absorb even more than that?

Also, how long before dinner should I drink my shake to avoid them being too close together thus constituting the same "sitting"?

ETA
I'm 5'10" 185 lbs if this matters.

I dont think that you will be able to find the correct answer to your question.

One must consider nitrogen levels when analizing how much protein the body needs. If you are in a cutting phase perhaps, your body would likly be getting less carbs, and perhaps fat, so one must compensate by eating more protein to allow for excess protein for the body to use since it is forced to  burn more than it usually would for fuel in the process.

There is really quite a bit to it, and it makes my head hurt, however I hope that that was not as non-sensical as it probably is.

That being said, I try to get at least 1g of protein per lb. of body weight per day when not in a cutting pahase. I eat 6 meals a day so I devide that up accordingly and eat about 40g of protein every 3 hours. I also take in 50-60gs devided up before and after my workout which I normally dont count toward my total.

Hope that helped.

My brother is an amateur body builder and I'm a power lifter.  General consensus with his trainers and my old coaches was 120 to 140 a day IF you do weight training.  That's spread out over 5 meals minimum each day.

there is no real research that shows an exact answer....I drink my shakes (usually 50-70g of protein per shake) and then a few hours later I eat a solid meal. I try to take in 1.5g of protein per lb......

I dont understand the too close together thing... you can eat one meal or all day long its not going to matter as to what you can absorb. Also you mean how much of the protein is absorbed from the intestines into the blood stream as far as absorbtion?  All of it.  As much as you can eat you will absorb.  Hundreds and hundreds of grams.  How much will you use to build muscle?  It varies on what you need right then.  Your body can use over a hundred grams at once for growth or it may only use a small percentage for growth.  Protein is more useful in your diet than just as a muscle building aid.  It is a good source of slow release carbohydrates and produces a meal with a better glycemic index too.

One gram of protein per pound of body weight. Divide that up by 6 meals per day. save last protein intake for right before bed time.