Using QtWebKit in your project
First of all you need to build QtWebKit (according to instructions for you OS), and install it (ninja install if you build with Ninja). In installation prefix you will get layout of directories, similar to what other Qt modules provide.
By default QtWebKit uses Qt installation root as its CMAKE_INSTALL_PREFIX. You may want to change this value if you don't want to overwrite existing QtWebKit module (if it's present).
As usual, just add QT += webkitwidgets or Qt += webkit to your .pro file.
However, to make this working when QtWebKit is installed outside of your Qt installation, you need to set QMAKEPATH variable in the environment or in .qmake.conf file.
For example, if your CMAKE_INSTALL_PREFIX in /usr/local, you need either to set QMAKEPATH=/usr/local in environment when you run qmake, or create .qmake.conf file in the same directory with your .pro file with the next contents:
QMAKEPATH += /usr/local
After you've installed QtWebKit into Qt installation prefix, all documented ways to use Qt modules from cmake should work. Read below if you are installed to different prefix.
When invoking cmake you need to add argument -DCMAKE_PREFIX_PATH=<installation prefix>, for example -DCMAKE_PREFIX_PATH=/usr/local. If you are already you using -DCMAKE_PREFIX_PATH= to specify path to Qt SDK, and it already has QtWebKit installed, prepend QtWebKit prefix path to Qt SDK path, and separate them with semicolon, e.g.
cmake .. -DCMAKE_PREFIX_PATH="/tmp/install-webkit;/opt/Qt5.4.0/5.4/gcc_64"
In your CMakeLists.txt use command like
find_package(Qt5WebKitWidgets)
to find QtWebKit, and command like
target_link_libraries(myapp Qt5::WebKitWidgets)
to use it in your application.
WARNING: Don't use qt5_use_modules(), it will force usage of QtWebKit installed within Qt SDK prefix.
pkg-config --cflags Qt5WebKit
pkg-config --lflags Qt5WebKitWidgets
You may need to set PKG_CONFIG_PATH to use it. pkg-config will also need to find core Qt libraries, in this case, like with cmake, put QtWebKit path before Qt path if you already have QtWebKit installed.