Motion blur is not something that you can enable or disable on per-object basis. Newer engine versions have a checkbox on translucent materials, allowing velocity writes, which may or may not help you. But overall, the answer you are looking for is that you can’t.
Yes, thank you, this seems to be a solution. In UE4.23+ there is an option inside the material.
But for this i need to upgrade my project to a new version. I guess for older versions you need to add velocity data for transparent materials in source code.