how can I build ubuntu linux kernel package ?

Why do you ask another question with the same contents?
You already have accepted the answer on https://answers.launchpad.net/ubuntu/+source/linux-signed/+question/697536
Do you expect different answers when you ask the same question again and again?

I didn't get usefull answers

Still the same answer:

You can't build the signed kernel package, because you do not have access to the signing key.
It would contradict the intentions of kernel signing if everybody could sign arbitrary software with the officially certified signature.

how can I access to the signing key?

Can you please just use ONE question rather than making a million questions. This isn't how forums work

how can I accessing to the singing key?

You can't.

why?

I need signed my ubuntu linux kernel

You have to distinguish two different kinds of kernel signing.

The official package linux-image-5.4.0-76-generic is signed with the signature key that is accepted by UEFI world-wide . There is no way that you can access that signing key, because it would contradict the intentions of kernel signing, if everybody could sign arbitrary software with the officially certified signature.

If you just want to create a private signature on kernel modules for loading them with secure boot, then you just have to create your own key, register it in the UEFI MOK database and sign the kernel modules with it. see https://wiki.ubuntu.com/UEFI/SecureBoot

how can I get the signature key ?

Which signature key do you want to get?

I want to get the signature key to signed ubuntu focal linux kernel any one.
I tried to checked out https://kernel.ubuntu.com/git/ubuntu/ubuntu-focal-signed.git
and following
fakeroot debian/rules binary

I didn't get signed debs
Thanks!

This is a kind of "master key" valid worldwide.
You cannot get access to that key.

When I following fakeroot debian/rules binary
those package can be created
block-modules-5.4.0-75-generic-di_5.4.0-75.84_arm64.udeb linux-tools-common_5.4.0-75.84_all.deb
crypto-modules-5.4.0-75-generic-di_5.4.0-75.84_arm64.udeb linux-tools-host_5.4.0-75.84_all.deb
debian.signed.all linux-udebs-generic_5.4.0-75.84_arm64.udeb
fat-modules-5.4.0-75-generic-di_5.4.0-75.84_arm64.udeb md-modules-5.4.0-75-generic-di_5.4.0-75.84_arm64.udeb
files message-modules-5.4.0-75-generic-di_5.4.0-75.84_arm64.udeb
fs-core-modules-5.4.0-75-generic-di_5.4.0-75.84_arm64.udeb mouse-modules-5.4.0-75-generic-di_5.4.0-75.84_arm64.udeb
fs-secondary-modules-5.4.0-75-generic-di_5.4.0-75.84_arm64.udeb multipath-modules-5.4.0-75-generic-di_5.4.0-75.84_arm64.udeb
ft_patch.tar.gz nfs-modules-5.4.0-75-generic-di_5.4.0-75.84_arm64.udeb
input-modules-5.4.0-75-generic-di_5.4.0-75.84_arm64.udeb nic-modules-5.4.0-75-generic-di_5.4.0-75.84_arm64.udeb
ipmi-modules-5.4.0-75-generic-di_5.4.0-75.84_arm64.udeb nic-shared-modules-5.4.0-75-generic-di_5.4.0-75.84_arm64.udeb
kernel-image-5.4.0-75-generic-di_5.4.0-75.84_arm64.udeb nic-usb-modules-5.4.0-75-generic-di_5.4.0-75.84_arm64.udeb
linux_5.4.0-75.84_arm64.tar.gz parport-modules-5.4.0-75-generic-di_5.4.0-75.84_arm64.udeb
linux-buildinfo-5.4.0-75-generic_5.4.0-75.84_arm64.deb plip-modules-5.4.0-75-generic-di_5.4.0-75.84_arm64.udeb
linux-cloud-tools-common_5.4.0-75.84_all.deb ppp-modules-5.4.0-75-generic-di_5.4.0-75.84_arm64.udeb
linux-doc_5.4.0-75.84_all.deb sata-modules-5.4.0-75-generic-di_5.4.0-75.84_arm64.udeb
linux-headers-5.4.0-75_5.4.0-75.84_all.deb scsi-modules-5.4.0-75-generic-di_5.4.0-75.84_arm64.udeb
linux-headers-5.4.0-75-generic_5.4.0-75.84_arm64.deb
linux-image-unsigned-5.4.0-75-generic_5.4.0-75.84_arm64.deb storage-core-modules-5.4.0-75-generic-di_5.4.0-75.84_arm64.udeb
linux-libc-dev_5.4.0-75.84_arm64.deb ubuntu-20.04-live-server-arm64.iso
linux-modules-5.4.0-75-generic_5.4.0-75.84_arm64.deb ubuntu-focal-signed
linux-modules-extra-5.4.0-75-generic_5.4.0-75.84_arm64.deb ubuntu-stable-focal
linux-source-5.4.0_5.4.0-75.84_all.deb usb-modules-5.4.0-75-generic-di_5.4.0-75.84_arm64.udeb
linux-tools-5.4.0-75_5.4.0-75.84_arm64.deb virtio-modules-5.4.0-75-generic-di_5.4.0-75.84_arm64.udeb
linux-tools-5.4.0-75-generic_5.4.0-75.84_arm64.deb

there is no linux-image-signed-5.4.0-75-generic_5.4.0-75.84_arm64.deb here

I have rewrite some codes,I want to use linux-image-signed-5.4.0-75-generic_5.4.0-75.84_arm64.deb to build custum ISO

Kernel module signing facility
https://www.kernel.org/doc/html/v4.10/admin-guide/module-signing.html

The Linux Kernel’s documentation
https://www.kernel.org/doc/html/v4.10/index.html
General Index : https://www.kernel.org/doc/html/v4.10/genindex.html

how does ubuntu signed the linux kernel?

A very limited group of canonical people has access to the signing key, but nobody else.

No way to signed the ubuntu kernel?

See my comment #9

Why don't you just take the current version of the signed kernel packages from Ubuntu?
Why do you need to modify the kernel?
Why do you need to sign that modified kernel?
Can't you use your private MOK signature if you need it signed?

5.4.0-75.84 is a example
The kernel doesn't supports u-boot booting,My fireware boot the kernel must signed

how can I reuse https://kernel.ubuntu.com/git/ubuntu/ubuntu-focal-signed.git/commit/?id=36e6973e2116e08aa2c6a4ff47f220de625b8ff1

.