Calculations of frequencies, transition rates, lineshapes and lightshifts of two-photon rotational transitions of HD+ in the ground vibrational state are presented. Two-photon rotational transitions can be addressed at high transition rates despite of the scarcity of sources of radiation in the THz spectral domain. A resonance-enhanced multiphoton dissociation detection scheme addresses the two-photon rotational transition (v,J)=(0,1)-<(0,2)-<(0,3) at 3.268 THz, the two-photon rovibrational transition (v,J)=(0,3)->4,2)->(9,3) at 1.4 μm and the photodissociation of (v,J)=(9,3) level at 512 nm on trapped and sympathetically cooled HD+ ions in the Lamb-Dicke regime. The photodissociated fraction of HD+ ions, modeled by rate equations, increases significantly at two-photon resonances when the rotational levels are coupled with the two-photon transition. A REMPD scheme with narrow-linewidth optical and THz sources may push the resolution of rotational spectroscopy at 4×10-13.