The Savitzky-Golay filter is not a discrete filter in the usual sense, and while all digital filters work best with uniformly-sampled data, it does not have that absolute requirement (the time vector or sampling frequency is not even a required argument).
The only way to determine the transfer function of the sgolayfilt function result is to take the fft of the output and divide it element-wise by the fft of the input, then plot the one-sided result to get the transfer function. Those signals ideally must be sampled regularly in order for the fft result to be meaningful. (The nufft function can be used for non-uniformly sampled data, however since all the other signal processing functions (that I am aware of) require uniformly-sampled data, it is best to resample them to a uniform sampling frequency if necessary before doing any signal processing on them.)
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