it appears you applied the expression in a wrong way. it would be easier to see what's wrong with a screenshots of your Timeline and Composition panels and showing the layers and values that you are trying to connect with expressions. also specify what exactly are you trying to accomplish.
Unterminated string constant here:
thisComp.layer("Sound Keys").effect("Sound Keys")("Output 3")"2
Sort out your quote marks and use the correct syntax.
what does that mean? what would the correct one be?
Strings always have to be opened & closed with quotation marks. When you type the first quotation mark "after effects" thinks you are going to enter a string so when you fail type the second quotation mark you get an "unterminated" string. Besides not making any sense even if it was temrinated, the "2 at the end of your expression is an unterminated string which is why you're getting an error telling you you have an untemrinated string. If you do not know what strings are, or what syntax is then you've got some research to do.
Even corrected your expression is not going to do much unless you properly set up Sound Keys. Once properly set up you should be able to just use the Pickwhip to create your expression.
You can find some good examples by typing Sound Keys in the search help field at the top right corner of AE. You should find some good tutorials on how to use that plug-in.
I would do that but now i get error 16 when i try to start ae i have looked online for a fix but the articles i have found don'y have a fix for windows 10
thisComp.layer("Sound Keys").effect("Sound Keys")("Output 3")+"2"
Thanks DULSARA DHANUKA