I am still interpreting the spectra and I tried to get the maximum of information out of it. I know that the spectrum is not corrected for the instrument response, small stars may be mistaken for a line that is not there and the signal to noise ratio of that picture taken is insufficient to analyse weaker lines, for instance H epsilon. The analysis may further complicated if the spectrum is not linear in terms of pixel vs. wavelength over a range of 300 to 800nm. Being aware of that, my interpretation may be a step too far but won’t stop me from analysing the data.
There are no perfect data in science!

On top of the graph the spectrum of WR136 is shown. The intensity of the spectrum is plotted as a function of wavelength between 350 and 750nm omitting the zero-order spectrum of the star. Three prominent spectral lines are marked with arrows pointing to the corresponding peaks in the graph below (He II at 468.6, H alpha at 656.3 and N IV at 710.9nm). In order to detect the elements in the stars atmosphere I identified as many spectral lines as possible. The spectrum indicates that the stars atmosphere is composed of nitrogen (annotated as blue lines in the graph), helium (red), argon (orange), hydrogen (black) and traces of carbon (green).
The presence of nitrogen can’t be questioned, the same holds true for hydrogen and helium. Weaker emission lines of these elements are likely responsible for the shoulders of certain peaks e.g. the C III and N III lines at 465 and 464nm close to the He II line at 468.6nm. In addition, Argon can be detected at 420.1nm and may be responsible for the rather strong H epsilon line, as it emits at 394.9 vs. 397nm. Another spectral line of hydrogen, H zeta at 388.9 coincides with a helium line at 388.8 and my therefore appear surprisingly strong. There is only one rather strong carbon line detected at 580nm.

I therefore conclude that the star consumed most of its hydrogen, the CNO-cycle has taken place and the star must have started the triple-alpha process (helium burning) long ago. This would explain the presence of helium, nitrogen and hydrogen. In addition, elements of the core and the outer layers must have exchanged by some sort of convection that for sure takes a while, otherwise the carbon and nitrogen should not be detected. The same holds true for the remaining hydrogen. Due to the presence of argon and the weak carbon lines, I conclude that the helium burning is almost finished and the alpha-process is forging heavier elements like argon while depleting carbon.
Taken together the core temperature of the star must be in the range of 100 to 200x10^6K for helium burning and necessitates at least half a solar mass. Depending on the mass, core densities around 1000g per cubic centimetre are required. The remaining lifetime of the star can differ significantly, from two million of years with 15 solar masses to just around 600 thousand years with 25 solar masses. Even if the star is massive enough for carbon burning, it will get a few hundred more years to live, neon and oxygen burning take a year to months and after that, it will detonate as a supernova. WR136 has 21 solar masses, therefore its life will end in a few hundred thousand years. With all the convection in mind, my guess is 200000 years ;-)