Which skills of programming should i posess to get a job in top it firms

Answer 1

Look at https://github.com/google - there are many their open-source projects. As you can find out they are using many various languages - Java, C++, Go, Dart, JavaScript, PHP, HTML, XML, CSS - almost everything.
I think more important think is to be clever - know computer science, algorithms etc.

Answer 2

It honestly depends on what you want to apply too at google. You should check out career options for them and the requirements. Not all jobs at google involve programming .