The MPS8598G is manufactured in a plastic TO-92 case. When looking at the flat side with the leads pointed downward, the three leads emerging from the transistor are, from left to right, the emitter, base, and collector leads. Here is an image showing the pin diagram of this transistor.
SMD Version of MPS8598G transistor
The FMMTA55 (SOT-23), KST55 (SOT-23), MMBTA55 (SOT-23), PZTA55 (SOT-223) and SMBTA55 (SOT-23) is the SMD version of the MPS8598G transistor. These transistors are of the same type, have similar parameters and are designed for surface mounting.
Replacement and Equivalent for MPS8598G transistor