What did Skobeltsyn publish about the possible existence of the positron? I've read across several sources that before C. Anderson discovered the positron in 1933 there were evidence of its existence pointed out previously by C.-Y. Chao and D. Skobeltsyn. After some rearch I found that a reference for the work of Chao here.
I wasn't able to find Skobeltsyn's work though. Could someone point it out for me?
 A: Skobeltzyn recounts his research on particle physics in his text "The early stages of cosmic ray particle research", which has been mentioned in another answer. I found it in the book The Birth of Particle Physics edited by Laurie M. Brown and Lillian Hoddeson in 1985.
It looks like he was the first one to try using Wilson chamber to detect tracks of high-energy electrons: "It appears that before my Wilson photographs were published nobody
had tried to observe the secondary $\beta$ particles of such hypothetical ultra
$\gamma$ rays." He also did measurements with magnetic field applied, but the field strength was too weak to reliably detect the radius of curvature of particle tracks. These results were reported in the paper suggested in another answer (D. Skobeltzyn, "Ueber eine neue Art sehr schneller $\beta$-Strahlen ," Z. Physik 54 (1929), 686-702).
Further in his text Skobeltzyn explains how this research eventually led to the discovery of positron, but nowhere he tries to take some credit for it, stating that repeating measurements in stronger magnetic field was the logical next step but that for a number of reasons he did not plan to do it.
A: According to Bazilevskaya's Skobeltsyn and the early years of cosmic particle physics in the Soviet Union paper (emphasis mine), 

Skobeltsyn demonstrated a series of photographs with the cosmic ray tracks at the Cambridge conference presided by Ernest Rutherford on 23–27 July 1928, where they made a strong impression on the audience. The comprehensive results were published in 1929 [14]. It is evident that Skobeltsyn’s work played a guiding part in the experiments that have led to the discovery of the positron. Sometimes people tell that Skobeltsyn could recognize the positrons on his photo plates. It was hardly possible with photographs that were at his disposal, at least because of the high requirements of Skobeltsyn to the purity of the experimental results.

where reference 14 is 

D. Skobeltsyn, Z. Phys. 54 (1929) 686.

At the time of writing, I could not find the actual reference, but this seems like it should be what you want/need.
A: You might want to look at D. SKOBELTZYN's paper
The Angular Distribution of Compton Recoil Electrons
Nature 123, 411-412 (16 March 1929) | doi:10.1038/123411a0;
but it is behind a 'paywall' and only a short abstract is available for free.
(FWIW, Nature, Lond., 1929, v. 123, No. 3098, p.411)
EDIT (11/27/2014):
See also: Dimitry V. SKOBELTZYN, THE EARLY STAGE OF COSMIC RAY PARTICLE RESEARCH, in: EARLY HISTORY OF COSMIC RAY STUDIES, Edited by YATARO SEKIDO and HARRY ELLIOT, Reidel, 1985, p.47:
"In November of 1931, when I was already in Leningrad, Millikan visited Europe and gave sensational lectures in Paris and Cambridge, showing a collection of Anderson's photographs. The main content of these lectures was published by Millikan, with Anderson as co-author, in May, 1932 (Millikan and Anderson, 1932). The tracks observed by Anderson were ascribed to high-energy protons produced by cosmic ray photons. In November and December, 1931, I received letters from Marie Curie and Fr$\acute{\textrm{e}}$d$\acute{\textrm{e}}$ric Jolio-Curie from Paris, and L. Harold Gray from Cambridge, who mentioned that they attended Millikan's lectures and in a few lines informed me of the results communicated by him. Somewhat more detailed information was given in the letter of Gray, with whom at that time I was in correspondence, discussing some problems of $\gamma$ ray research. He wrote (November 27): "I think (my emphasis) that in every case the proton tracks were more dense than those of electrons". That probably was his imagination. Millikan showed to his audience some eleven pictures of good tracks in the range of 20-80 MeV energy, say E ~ 50 MeV on the average.
Now, the ionisation density (specific ionisation) depends mainly on the velocity of
the particle, or on the quantity $E/mc^2$, where $m$ is the proper mass of the particle.
With this quantity given, the absolute value of the mass $m$ of a particle of given charge
has but little importance. It follows that the ionisation produced by a proton of 50 MeV is practically the same as that of an electron of about 25 keV. It is impossible to confuse the specific ionisation of such a slow electron with the ionisation of a fast
("relativistic") one, having several MeV or more. However, the positive tracks on
pictures demonstrated by Millikan did not differ essentially from electron tracks on the
same pictures, with the energies of about 50 MeV. Prof. Millikan and his audience
overlooked this incosistency. After I received Joiot's letter, I wrote him straightforwardly my views on the subject and suggested that something was wrong with
Millikan's photos or their interpretation."
