Is there a particular Cygwin package I need to install for top?
You need the procps package.
How can I find out which package top is in?
The easiest way to find the package containing a particular command or file is to use the Cygwin Package Search page:
Open the Cygwin Package Search web page in your web browser.

Select either the 32 bit or 64 bit version of Cygwin.
Enter the name of the program you are looking for (top).
Press "Go" on the web page.
In this case, entering just top matches many (2475) packages (for most commands there are fewer matches).

So let's try entering the function of the command instead of its name:
Enter the function of the program you are look for (process monitor).
Press "Go" on the web page.

Now we have a more manageable list ( 8 matches) and we can easily see that the required package is probably:
procps-3.2.8-5 - procps: System and process monitoring utilities (installed binaries and support files)
Click on procps-3.2.8-5 to make sure we have the correct package and we can see:
2016-01-25 10:20 90643 usr/bin/top.exe
