how to find out the compession ratio pinto 2L

To do it accurately requires a lot of careful measurement.
 
You need to determine the combustion chamber volume by taking the head off, having both valves closed, spark plug in, and filling the chamber with fluid.  The face of the chamber needs to be sealed, usually with a piece of perspex with a small hole in it for the fluid to enter.  A burette or pipette is needed to do this accurately.
 
You also need to determine the volume of the gasket.  For instance, your gasket may measure 93mm wide, and be 1.6mm thick when compressed, which gives it a volume of 10.87cc (cubic centimeters)
 
Then there is the deck volume, which is how much space is there between the top of the piston and the top of the block.  This can be a negative number if the pistons protrude from the top of the deck.
 
Another figure you need is the volume above the top ring.  I've seen 1 cc used as an estimate, as it is hard to accurately measure.
 
All of the above added together comprises the volume above the piston.
 
Throw in the swept volume of the cylinder, which is derived from the bore and stroke of the engine (both of which can be measured if need be), and your compression ratio is calculated from the volume above the piston divided by the sum of the swept volume of the cylinder and the volume above the piston.
 
That's it in a nutshell (assuming I haven't forgotten anything).