I need to make a small modification to the source code, and want to check for a specific survey ID. Can someone provide the code snippet to do this?

Basically, I want to check for :

IF CurrentsurveyID = 123456, then
do something
Endif

So just need to know how to get value of CurrentsurveyID

Isn't {SID} working, to get the surveyid?

Thanks, I mean in the PHP source code...

I came across examples like $surveyid = $oSurvey->sid; -- which makes me think that $oSurvey->sid is what I would use...

Why are you modifying the source code? Can whatever you want done be accomplished in the theme TWIG files. That would be safer.