What should you learn first? As always the answer is "it depends"
If you are more interested in the java programming side of things, then I would suggest catching up with the changes in the java language since you last touched it.
New Features & APIs etc.
I would also recommend you get acquainted with Spring and Spring boot. which have some quick start modules and examples.
JDBC is still there.
But must of the time I want to talk to a database I use an ORM tool like Hibernate to abstract away the JDBC code.
And Spring provides a nifty feature such that you annotate your bean, write an interface that extends a org.springframework.data.repository.Repository and you're done.
You don't actually end up writing any jdbc code at all.
If you are interested in the web side of things, then brush up your javascript (not the same as java)
And then check out a framework such as
Angular or React.
In terms of this project, you could actually do both, which might also help you on the way to understanding how web applications have evolved.
#1 - Write back end java classes to load/save your data from your database. (spring boot data module)
#2 - Build a JSP/Servlet Web application with a form that lets you interact with the back end java code. (Spring MVC)
#3 - Write a REST web service that exposes the back end java code (spring-boot)
#4 - Build a "Single page app" in javascript that does exactly the same as your JSP web application, just without JSP. (angular/react)
The bits provided in brackets are suggestions only to help 'automate' the work.
But personally I would be more impressed by a demo that utilized the frameworks out in the real world rather than having custom written java code behind them.