Are you planning to upgrade your WebLogic Server environment from an older 11g environment (e.g. 10.3.2 - 10.3.5) to 10.3.6? If this is the case, the wls1036_upgrade_generic.jar is only available through a downloadable patch via My Oracle Support (https://support.oracle.com). You will need to have an OTN license to be able to download patches from My Oracle Support (MOS). If you are able to download patches, search for patch number 13529623 in Patches & Updates. For detailed steps on how to download the WLS upgrade, you may use section 2.2 of this KB article http://pitss.com/us/2013/02/22/11gr2-11-1-2-0-to-11-1-2-1-forms-upgrade-prerequisites-for-windows/ as a guide (the jar file to download is the same for Linux, Solaris, IBM AIX, etc.).
If you are looking to install Oracle WebLogic server for the first time, you may use https://edelivery.oracle.com if you have purchased WebLogic Server or http://www.oracle.com/technetwork/middleware/ias/downloads/wls-main-097127.html using an OTN license if you plan to use WebLogic for development/testing purposes. Hope this helps!