Child Theme Attribution
 

I have Lifestyle child theme, I just want to know can i create a new child theme by using that theme and what Attributions i should not remove?

you can make a new theme. In the style.css file do not change in any way the template: genesis line. Doing so will break things. Otherwise you can change anything else.

Responsive Navigation
 

how can i switch menus to <select></select> in mobile responsive?

Please start a new thread for any new questions you have. Thanks.