There are several different methods to check what version is installed, two of them are:
Go to System Preferences > Flash Player > Updates tab. There are 2 variants of Flash Player on Mac, NPAPI for Safari and Firefox, and PPAPI for Opera and Chromium-based browsers, and both will be listed in the 'Updates' tab.
If Flash Player is installed the version installed will be listed here. If there is a version listed, click the Check Now button and Flash Player will check for an update. If an update is available a notification dialog will display.
If there isn't a version listed, then Flash Player isn't installed. Click the Install Now button to launch the browser to the download page. Download and install Flash Player.
If Flash Player is not installed, a "Missing Plug-in" message will display where Flash content should display.
Click the "Missing Plug-in" text and a window displays indicating Flash Player is required displays.
Click More Info button to be direct to the download page to download and install Flash Player
If a previous version of Flash Player is detected, and Safari has blocked it, click the "Flash out-of-date" text and a windows displays indicating Flash is out-of-date displays. Click Download Flash... button to be directed to the download page to download and install the latest version.