The pkg list command will tell you if a package is installed, frozen, obsolete or renamed under the column IFO.

I "i" = Package is installed
F "f" = If a package is frozen, you can only install or update to packages that match the frozen version.
O "r" = It indicates that package has been renamed.
O "o" = It indicates that package is obsolete. You cannot install a package that is marked obsolete.

reny@solaris11_2:~$ pkg list gedit
NAME (PUBLISHER)                                  VERSION                    IFO
editor/gedit                                      2.30.4-         i--

or with verbose -v to display complete package:

reny@solaris11_2:~$ pkg list -v gedit
FMRI                                                                                                                                 IFO
pkg://solaris/editor/gedit@2.30.4,5.11-     i--

If you don't know the name of the package, but know the name of the application that you would like to install use the search command:

reny@solaris11_2:~$ pkg search file::gedit
basename   file   usr/bin/gedit pkg:/editor/gedit@2.30.4-

Use the info command to display more information about an installed package:

reny@solaris11_2:~$ pkg info gedit
Name: editor/gedit
Summary: GNOME text editor
Category: Applications/Accessories (org.opensolaris.category.2008)
Development/Editors (org.opensolaris.category.2008)
State: Installed
Publisher: solaris
Version: 2.30.4
Build Release: 5.11
Packaging Date: October 28, 2013 02:56:32 PM
Size: 9.70 MB
FMRI: pkg://solaris/editor/gedit@2.30.4,5.11-

For more information about packages in Solaris click here.