Should I show my project at work on my Online Portfolio?

Depending on your level NDA, you may have to think beyond the project.

Write a blog post about what you learned working for Company X to show your expertise.
Come up with a side project in which you demonstrate similar skills as in your protected project.
List Company X in the clients section of your portfolio, to show you have worked for them.

How you finally decide to alternatively present your value really depends on the value you originally intended to show.

Non-Disclosure Agreements are not an excuse for an empty portfolio. You need to identify the value of your protected material and look for alternative ways to communicate this.
Your project is like a story, don’t take people out of this. Rather than censoring content, replace it. This may require you to create fictional, dummy content.