Often I see things in recipes where they rely on things like "virtual/kernel". But how do I know what bitbake recipe virtual/kernel points to?
Usually you can find this information in the machine configuration file. This isn't always guaranteed, it could be stashed in some other configuration file like the distro configuration file (i.e. Angstrom defines the PREFERRED_PROVIDER_virtual/update-alternatives)
In the case of the dm3730-am3715-evm machine type its configuration file specifies:
PREFERRED_PROVIDER_virtual/kernel = "linux-omap-psp"
This tells me that if I were to "bitbake virtual/kernel" it would look for the latest linux-omap-psp recipe and build that with the exception of whether or not that recipe set DEFAULT_PREFERENCE to -1. If so then it would look for the next version of linux-omap-psp.
So in general the virtual/xyz values are set in the configuration files. You could of course always just "bitbake virtual/xyz" and see what it builds, but if you have a slow system like mine sometime you want to know without waiting on a build :)