Tomonaga-Luttinger liquids (TLLs) have been predicted to host fractional excitations, which are emergent exotic particles that separate the spin and the charge of electrons. This phenomenon is commonly referred to as the spin-charge separation, which is a key to understanding electron correlation effects. Much work on TLLs has focused on collective response of the fractional excitations, but direct imaging or local spectroscopy of them is quite challenging due to their fractional nature. In this talk I will present our recent studies on a 1D interacting system: mirror twin boundaries (MTBs) of single-layer 1H-MoSe2. We fabricate semiconducting SL 1H-MoSe2 devices whose MTBs host confined 1D electron gas. The gate-dependent STM spectroscopy of MTBs allows direct measurement of the Coulomb interaction energy, which reveals electron correlation effects and suggests TLL behavior. Then the collective spin and charge density wave excitations predicted by the TLL theory is clearly resolved by two linear dispersion branches in the observed Fourier spectroscopy. The velocities of the fractional spin and charge bosons are in quantitative agreement with the TLL theory.