I was making the "Differential abundance analysis with gneiss" tutorial and I want to know if it's possible to asses the value of log-abundance for each square of the heat-map. I want to asses the variability of OTU's abundance for each subject and evaluate temporal stability of the microbiota as they do in this paper:
What you are describing is a fairly customized plot. Gneiss heatmap does not have an option to overlay text on the plot. To re-make this plot you will need to export the data from your files and make the plot externally, e.g., in R.