How can I find out the screen resolution and dpi on my mac book pro?

Open the Apple menu at the very top-left of the screen and click on About This Mac. Click on the More Info button, which will open up a window with lots of categories of information. The Graphics/Displays category will tell you your screen resolution.

If you like terminal, then you can get via below command

system_profiler SPDisplaysDataType |grep Resolution

For example

>system_profiler SPDisplaysDataType |grep Resolution
          Resolution: 1920 x 1080 @ 60 Hz

This depends on the model of Macbook Pro (i.e. the screen size - 13.3", 15.4" or 17") you purchased, but the resolution and DPI (or PPI), for the 2009 unibody models, is provided by Wikipedia (here and here).

However, given the resolution and display size, you can easily calculate the PPI. In summary:

MacBook Pro 13.3":  1440x900 (127.68 PPI)
MacBook Pro 15.4":  1440x900 (110.27 PPI)
MacBook Pro 15.4":  1680x1050 (128 PPI)
MacBook Pro 17":    1920x1200 (133.19 PPI)