Is it obligatory to perform ghusl upon feeling the emission of semen, despite not seeing it except as usual yellowish discharge, especially when this sensation recurs several times daily?

You are not required to perform ghusl (ritual purification) if you doubt the emission of semen and its mixing with yellow discharge, for the default is that it has not exited. Likewise, according to the majority of scholars, ghusl is not obligatory if you are certain that semen has separated from its place but has not exited the body.