It is generally possible to add another RAM stick to your laptop, but it's important to make sure that the new RAM is compatible with your laptop's existing RAM. Ideally, you should try to match the brand, speed, and timings of the existing RAM as closely as possible to ensure that the two sticks work well together.
As for the amount of RAM you should add, it really depends on your usage. If you're using memory-intensive applications like video editing software or virtual machines, then having more than 16GB of RAM can be beneficial. However, if you're only using your laptop for basic tasks like web browsing and word processing, then 16GB of RAM may be overkill.
If you do decide to add another stick of RAM, it's generally recommended to go with a matched set of 2x8GB sticks for optimal performance in dual-channel mode. However, if you're on a tight budget, adding a single 8GB stick to your existing 8GB stick should still give you a boost in performance.
Ultimately, it's up to you to decide whether the cost and potential performance boost are worth it for your specific usage.