Hi Rakesh,
You can find the sl_sdk.jar at the following location
C:\Program Files\SAP BusinessObjects\SAP BusinessObjects Enterprise XI 4.0\SL SDK\java\sl_sdk.jar
The sl_sdk.jar comntains a manifest.mf mile which contains the referrences to all the other required files.
Make sure you have Client installed on your machine to work with SL SDKs as you would need to set the path of Connection Server as well.
Thanks,
Prithvi