What's the latest Macbook Pro that can run my Snow Leopard HD?

In fact all MBP models prior to the "late 2011" models can boot Snow Leopard.

With one glaring exception, the retail Snow Leopard 10.6.3 installer disc can't be used on them. You have to find a system specific 10.6 disc that shipped with them, or a bootable copy of 10.6.8 to clone over to them.

At least the data files and applications should work on any Mac released prior to Lion. For some of these Macs, you will need the security updates and combo updates for Snow Leopard, if they weren't already installed.

With Lion's release the significant difference is the fact that PowerPC applications made for Mac OS X do not have a Rosetta I environment to work to work with,which is discussed in more detail on my tip with the link to Lion above.

Cloning the hard drive is possible, although you may have to force the hard drive to format HFS Extended GUID, as APFS, the default formatting for solid state and flash drives, on High SIerra and later, and the required formatting on Mojave will render these drives invisible to anything with less than High Sierra.

If you have a cloned backup and you want to bring it up to a newer Mac, you can connect the drive to the newer Mac than Snow Leopard and use the Migration or Setup Assistant. Keep in mind any old PowerPC applications will need an Intel Mac equivalent title. AppleWorks will not run natively on Lion and later Macs without Snow Leopard Server (not client), installed on a virtualization client like Parallels.

Is it the Retail version & which version?

MBP 13" Mid 2010...

Mac OS X 10.6.3 (10D2125)

Later OSMac OS X 10.6.4 (10F2108)

Maximum OSmacOS 10.13.6 (17G65)

But if you have 10.6.0 then MBP 13", 15", 17" Mid 2009

"What's the latest Macbook Pro that can BOOT FROM my Snow Leopard HD?"

I will take the liberty of rewording that question to "what's the latest MacBook Pro that can boot Snow Leopard" since we cannot be certain just what your Snow Leopard HD contains.

The answer to that more generic question is an early 2011 model, more specifically a MacBookPro8,3.

Adding to some confusion is the fact a MacBookPro8,1 is later than an "early 2011 model" and it won't boot Snow Leopard.

In fact all MBP models prior to the "late 2011" models can boot Snow Leopard.

Good point, a Mac can't boot from an OS that is older than its release. Which leaves many people with newer than March 15, 2010 Macs in a bit of a quandry if they don't have the original installer discs that shipped with the Mac, or a Mac released at the same time as their Mac. The retail release won't run on newer Macs.