  We suggest to study the production mechanism and some details of the
production properties to probe the structure of the DDpi resonance T_cc^+
recently observed by the LHCb Collaboration. If the resonance is produced as a
four-quark state, one can find the corresponding finger prints via measurements
on some production properties that are the same as those of Xi_cc. The reason
is that a special colour connection on the interface between the perturbative
and non perturbative QCD is required for these doubly-charm hadron production.
On the other hand, if T_cc^+ is produced as a hadron molecule, the measurement
on the momentum correlation of DD^* can be a smoking gun to make the judgement.
The present data favour a compact four-quark state production via the cc
diquark fragmentation.
