Many questions describe hypothetical biochemistries, or alternatives to carbon, water, DNA, etc that aliens could use.
They cite specific examples, given a world we know about, of what creatures would need to metabolize. For example:
(Titan's environment): Low temperature. 45% larger atmospheric pressure than Earth. Methane and ethane are the solvents. Carbon-based life which breathes methane and ethane and expels acetylene. Other possibility is breathing hydrogen, ethane and acetylene, producing methane.
-Victor Stafusa, on link at start of question
What if we don't know a ton about the planet or moon we are designing, ex. the intricacies of atmospheric composition, the exact pressure, - but we want to get a sense of what our organisms should respire or consume, given a biochemistry? Is there even a way? Do you just pick what's abundant?
In other words
Could I say "The species has genetic material containing y" and get a list of things it will most likely eat?