This slideshow requires JavaScript.

So, where did you get this slideshow code?

I just create a gallery from Media Library…

Sounds like an issue with your theme. You can get support for your theme from here: https://wpbandit.com

I have changed many themes to fix this problem. But it won’t changed. Shows same saying “This slideshow requires JavaScript” before slideshow..

Let’s see the page with the issue while you’re using the Twenty Fifteen theme.

Same problem is there….

Okay so this is the Jetpack plugin’s slideshow. This isn’t a theme problem. You need to create a support thread on your plugin’s support section here: https://www.ads-software.com/support/plugin/jetpack#postform