Calculating maximum signal frequency knowing its sampling rate?
The maximum possible frequency in the sampled signal is half the sampling rate, assuming that you are not bandpass sampling and/or there is an anti-aliasing filter. The question is whether the signal has content up to that rate or whether it stops at a lower frequency.

One way to determine this would be to take your sampled signal $x[n]$ and transform it to the frequency domain via FFT to get $X[k]$.

Then find the largest value of $k$ for which
$$
\left |X[k] \right| &gt; t
$$
for $0 \le k \le \frac{K}{2}$ where $K$ is the length of $X$ and $t$ is some "threshold" below which you decide the signal level is effectively zero.