How can I read my transistor part number?
I would guess this is a 40N65, a 40 A, 650 V IGBT with integrated antiparallel diode. Infineon makes them, and I would guess that yours is likely to be a second-source one from a manufacturer that doesn't sell to the general public.
They're a fairly expensive device, at $4.44 apiece from Digi-key, so I'd suggest you be sure you need this specific device and can't substitute a different one before buying them.

In general, when you have a part number that you don't recognise and searching the web doesn't find any matches, it's a good idea to strip off any trailing letters, and sometimes also initial letters.
Many manufacturers will add various letters to the end of a part number to indicate whatever random variant they think is worth indicating (for example, one might indicate that it's a lead-free device, or perhaps that it's in a TO-263 package rather than a TO-252, or it's an enhanced version with better specs, or whatever). Many others will also add some letters that represent their specific company to the beginning; Analog Devices will use AD, International Rectifier will use IR, and so on.
Removing these to find the base part number can help you find the same part from other manufacturers who use different naming schemes around the same base part number.