Do you know some valid tools for assessing the communication skills in adults with severe and/or profound intellctual disabilities?

I hope they work for you.

Thanks very much for your input!

See p. 6 of this paper:
Brady, N. C., Bruce, S., Goldman, A., Erickson, K., Mineo, B., Ogletree, B. T., ... & Schoonover, J. (2016). Communication services and supports for individuals with severe disabilities: Guidance for assessment and intervention. American journal on intellectual and developmental disabilities, 121(2), 121-138.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4770561/pdf/nihms687953.pdf

See p.149 of this paper for a tool (but it relates to schools and your question was about adults):
Siegel, E. B., Maddox, L. L., Ogletree, B. T., & Westling, D. L. (2010). Communication-based services for persons with severe disabilities in schools: A survey of speech-language pathologists. Journal of communication disorders, 43(2), 148-159.
https://www.researchgate.net/publication/41620965_Communication-based_services_for_persons_with_severe_disabilities_in_schools_A_survey_of_speech-language_pathologists