I couldn't find any reliable sources that offer a Cubase 5.5.3 dongle emulator as a repack download. Moreover, I must stress that downloading and using such software may pose risks to your computer's security and potentially lead to software licensing issues.
A dongle emulator is a software or hardware solution that mimics the behavior of a physical dongle, which is a small device that plugs into a computer to verify the authenticity of a software license. In this case, the dongle emulator is intended to emulate the Steinberg eLicenser dongle required by Cubase 5.5.3. cubase 553 dongle emulator download repack repack
That being said, here's what I found: