fs = 44100;
fftSize = 1024;
signal = randn(fftSize, 1); % as an example
spec = fft(signal, fftSize);

frequencies = 0:fftSize/fs:fs-fftSize/fs;

logMagnitudeSpec = 20*log10(abs(spec));

figure;
plot(logMagnitudeSpec)

[peakValues, peakIndizes] = findpeaks(logMagnitudeSpec, 'NPeaks', 2);

disp(['Two largest peaks at f_1=' num2str(frequencies(peakIndizes(1))) ...
    ', f_2=' num2str(frequencies(peakIndizes(2)))])