Is there a kernel 5.8 ppa for ubuntu 20.04?

You can install the 5.8 kernel to Ubuntu 20.04 now by running

sudo apt install linux-generic-hwe-20.04-edge

The kernel will get updates.

But if you wait some time (it is a matter of days) linux-generic-hwe-20.04 (without edge) will also pull the 5.8 kernel.

Update: Now we have linux-generic-hwe-20.04 pointing to the 5.8 kernel. If you've installed the edge, it is better to remove it by

sudo apt remove linux-{image,headers}-generic-hwe-20.04-edge
sudo apt install linux-generic-hwe-20.04

If you want to use different kernels, you can also use the Ubuntu Mainline Kernel Installer. This will let you pick from a variety of kernels, usually long before they make it to Ubuntu's defaults. So, we can add this to the list of choices you can make.

It's pretty straightforward.

sudo add-apt-repository ppa:cappelikan/ppa
sudo apt update
sudo apt install mainline

From there, you just open the application and pick the kernel you'd like to use, install it, and then reboot to use the new kernel. It is fairly intuitive and looks a bit like this:

The app can be rather annoying with multiple notifications. You can change the frequency of checks in the application's settings. You can also click on 'changes' and see what changes (the changelog) have been made to the kernels.