The equery tool is used for viewing package information.

list what package FILES belong to
list changelog entries for ATOM
verify checksums and timestamps for PKG
list all packages directly depending on ATOM
display a tree of all dependencies for PKG
list all files installed by PKG
list all packages for matching ENVIRONMENT data stored in /var/db/pkg
list all packages that have USE flag
display keywords for specified PKG
list package matching PKG
display metadata about PKG
display total size of all files owned by PKG
display USE flags for PKG
print full path to ebuild for PKG

Show Package Files

~ $ equery files pciutils
~ $ equery files dev-lang/php

Show Package Size

~ $ equery size pciutils
~ $ equery s dev-lang/php

Which Package Owns File

~ $ equery belongs /usr/bin/which
~ $ equery b
~ $ equery b $(which awk)