Ruthenium compounds serve as a platform for fundamental concepts such as spin-triplet superconductivity(1), Kitaev spin liquids(2-5) and solid-state analogues of the Higgs mode in particle physics(6,7). However, basic questions about the electronic structure of ruthenates remain unanswered, because several key parameters (including Hund's coupling, spin-orbit coupling and exchange interactions) are comparable in magnitude and their interplay is poorly understood, partly due to difficulties in synthesizing large single crystals for spectro-scopic experiments. Here we introduce a resonant inelastic X-ray scattering (RIXS)(8,9) technique capable of probing collective modes in microcrystals of 4d electron materials. We observe spin waves and spin-state transitions in the honeycomb antiferromagnet SrRu2O6 (ref. (10)) and use the extracted exchange interactions and measured magnon gap to explain its high Neel temperature(11-16). We expect that the RIXS method presented here will enable momentum-resolved spectroscopy of a large class of 4d transition-metal compounds.