There is no quantifiable E-A-T score in the sense that it can be directly measured and improved. Google’s Gary Illyes indicated in his 2019 Q&A with Marie Haynes that Google does not have an internal E-A-T score. However, if there was an "E-A-T score", it would come from judging the page quality of a web page and its author - based on their Expertise, Authoritativeness and Trustworthiness. So by focusing on strengthening those signals, it follows that your E-A-T score would improve.