  Many attempts have already been made for detecting exomoons around transiting
exoplanets but the first confirmed discovery is still pending. The experience
that have been gathered so far allow us to better optimize future space
telescopes for this challenge, already during the development phase. In this
paper we focus on the forthcoming CHaraterising ExOPlanet Satellite
(CHEOPS),describing an optimized decision algorithm with step-by-step
evaluation, and calculating the number of required transits for an exomoon
detection for various planet-moon configurations that can be observable by
CHEOPS. We explore the most efficient way for such an observation which
minimizes the cost in observing time. Our study is based on PTV observations
(photocentric transit timing variation, Szab\'o et al. 2006) in simulated
CHEOPS data, but the recipe does not depend on the actual detection method, and
it can be substituted with e.g. the photodynamical method for later
applications. Using the current state-of-the-art level simulation of CHEOPS
data we analyzed transit observation sets for different star-planet-moon
configurations and performed a bootstrap analysis to determine their detection
statistics. We have found that the detection limit is around an Earth-sized
moon. In the case of favorable spatial configurations, systems with at least
such a large moon and with at least Neptune-sized planet, 80\% detection chance
requires at least 5-6 transit observations on average. There is also non-zero
chance in the case of smaller moons, but the detection statistics deteriorates
rapidly, while the necessary transit measurements increase fast. (abridged)
