Stock blow off vavle
 

I am just curious about whether there is a stock blow off valve, or if one can be added in. If there is one stock, where is the location of it.

there is and it vents back into the intake. Not sure of your model - see if RobertDIY's vid helps

Its a 2001 V70 XC 2.4 Turbo, not sure if that can give you any more of an idea on its location...

It should be right on the side of the turbo housing - round thingy with a vacuum line. Its job is to vent the boost back into the exhaust when you go off throttle to reduce strain on the turbo. Many after market BOVs vent into the atmosphere, thus the tell tale "woosh" sound. there's a diaphram inside that can tear and leak boost - repair kits are $20 or so.