I feel like spectroscopy would only give you suggestive evidence of life at best, like if significant quantities of oxygen were detected in the atmosphere of an Earth-like exoplanet in the habitable zone. I think your best bet for direct detection of life would come from Mars rover or maybe a mission to one of the Jovian moons (but AFAIK no probe will arrive at a Jovian moon in this decade). Not sure either will detect life in this decade, but I sincerely hope you win your bet!