I have heard ajax and jquery are good options but apparently jquery is loosing relevance in web development.
This is too broad a question, inviting replies that are too subjective.
Where are you currently at in your learning journey?
What specific use case do you have in mind? A fully reactive application type of site, or something with just a tiny dynamic element that needs updating?
But… jQuery is fine and actually pretty great. I wouldn’t dismiss it as a beginner if you just need to get a job done. jQuery powers an extraordinary number of websites.