That's a tuff question that the answer could fill hundreds of books. The most important skill would be how to find the information you need to fulfill the task in Internet marketing you are trying to fill.
Digital marketing experts need to have a variety of skills in order to be successful. First and foremost, they need to be able to understand the digital landscape and how it changes constantly. They also need to be able to create effective marketing campaigns that reach the target audience. Additionally, digital marketing experts need to be able to analyze data in order to track results and optimize campaigns. Finally, they also need strong communication skills in order to collaborate with other team members.
Skills Needed to Become a Digital Marketing Expert are:
-Use of social media
-SEO and SEM
-Skills in Basic Design
And need to work on it by gaining knowledge
The best way to find out is to do a search on indeed for digital marketing and see what the requirements are for the roles available.
Google offers certificates for Google Ads and Analytics. Microsoft also offers courses and certifications for its advertising platform. A lot of the jobs will require you to have a solid understanding of Google Ads and Google Analytics, so I recommend looking into that.
Obviously, you need to get experience. So get a client, or start marketing your own website to get SEO and social media marketing experience. Learn about buyer personas and keyword research. There is a Fundamentals of Digital Marketing course that's available for free, and its created by Google - even comes with a certificate. Google it - and take the course ASAP.
I recommend learning WordPress well. Shopify too if you have time to learn both or if you already know one well.
In my opinion is important to have analytics skills, be a good communicator, be open to changes, and be curious to learn every time. Before these soft skill will follow the skills, you develop into applications that are useful for this job (social media platforms, SEO, SEM,etc)