Also other OS (other linux distro) not detected by KaOS grub efi. Install KaOS with GPT/EFI scheme, but when choose efi partition, it won't show /boot/efi or flag esp and boot, just only show /boot or boot flag. KaOS efi boot show on BIOS/EUFI, but not detected by other linux OS.

KaOS does not use GRUB for EFI , it uses systemd-boot, nor uses /boot/efi for the ESP, but rather /boot as recommended upstream.
Windows and other Linux distros will be automatically added to the boot menu, if they use the same ESP.
See every news article and included release notes for KaOS ISOs, to learn more about systemd-boot see:
https://www.freedesktop.org/wiki/Software/systemd/systemd-boot/

I have Manjaro installed, it detected by command "sudo update-grub"
]$ sudo grub-install
[sudo] password for leokusuma:
Installing for x86_64-efi platform.
Installation finished. No error reported.
]$ sudo update-grub
Generating grub configuration file ...
Found theme: /usr/share/grub/themes/manjaro/theme.txt
Found linux image: /boot/vmlinuz-5.8-x86_64
Found initrd image: /boot/intel-ucode.img /boot/initramfs-5.8-x86_64.img
Found initrd fallback image: /boot/initramfs-5.8-x86_64-fallback.img
Found Windows Boot Manager on /dev/sda1@/EFI/Microsoft/Boot/bootmgfw.efi
Found KaOS (2020) on /dev/sda6
Adding boot menu entry for UEFI Firmware Settings ...
Found memtest86+ image: /boot/memtest86+/memtest.bin
done
but KaOS boot entry still not show on Manjaro Grub.

Not clear what the way some other distro handles their bootloader has to do with KaOS. As the command shows, KaOS is found. As said, there is no GRUB for EFI in a standard KaOS install.

Provide output of 'sudo blkid'
Then tell us what partition is KaOS /boot partition and KaOS root partition (sda6?)
Also what is manjaro /boot/efi partition and windows EFI partition (sda1?).

I assume you want to use Manjaro grub to boot KaOS. Tell us if it is not so (more dificult to use KaOS systemd-boot to boot all other OS if their EFI partition is not the same partition as KaOS, but can be done).

I'm really sorry for my newbie. It works now by following this article from (old) Manjaro Forum.