Are there any relations between stress and sonority? Does stress denote high sonority?
There is plenty of controversy over what "sonority" is, and whether it is a real thing (what is it a thing in/of?). Typically, "sonority" is invoked with respect to segment sequencing, where it is said that sonority increases within the syllable to a peak, then decreases. Accordingly, in a syllable like (hypothetical) [prjawŋk], the least sonorous segments are /p,k/ and the most sonorous is /a/. The phonetic property most often correlated with sonority (which is a phonological concept) is openness of the vocal tract, where the vocal tract has the maximum resonance potential. Stress is primarily the result of laryngeal manipulations which don't effect resonance, but which are relevant to the loudness and thus perceptibility / salience of the sound coming out of the mouth.
It has been proposed, in fact, that vowels can differ in abstract phonological sonority, and that some stress systems are sensitive to sonority. However, that proposal is controversial, see recent papers by Shu-hao Shih for discussion. The main problem is non-circularly measuring the sonority of a particular segment.