$\Omega^0_c \to \Sigma^+ K^-K^- \pi^+$ Feynman diagram How can I work out the Feynman diagram for the decay process, $\Omega^0_c \to \Sigma^+ K^-K^- \pi^+$?
 A: Start by identifying the constituents of each particle. The charmed baryon $\Omega^0_c$ is $ssc$, that is, two strange quarks and a charm quark. The sigma baryon $\Sigma^+$ is $uus$, the kaon $K^-$ is $s\bar u$ and the pion is $u\bar d.$ Thus, you know the initial and final particles in your diagram. 
You can now use the Feynman rules of the Standard Model to work out the interactions to include, which are allowed. In some cases, processes may be mediated by the weak or electromagnetic interaction; either can be used for a diagram, though one will usually be more probable. 
To check which is in a particular case more probable, you will need to check the branching ratios from the Particle Data Group. 
Thanks to anna v for the useful link to quark flavour transformations; you can use these to see which interactions to pick in order to get the right flavours in the final state.
Just a minor caveat; this will not be the Feynman diagram for the process. Remember this is all at tree level, and you could consider arbitrary numbers of loops as well though the dominant contribution I believe for this process is at tree level.
