I need a way to put any chosen window to be always on top. For example, if I read a book in iBooks or I'm writing code in XCode using Sublime Text. I want a application or way to overcome the issue. I tried Helium and Fluid Browser but they are like web browser it's not I look for. I exactly want any application to be on top always for High Sierra.
Try Deskovery3. It does that and more.
There's also Afloat: http://www.perfectlyrandom.org/2016/10/23/always-on-top-in-macos-sierra/
Note: these require you to temporarily lower the security settings on your Mac (disabling SIP) during part of the installation/setup.
Alternatively, you might want to investigate the following macOS features: Full Screen, Mission Control, Hot Corners and Spaces which all allow easy and flexible control of application windows.