I suggest you do a web search on the ETF name you have in mind with the word "prospectus", or, better yet search on
https://www.sec.gov/edgar/searchedgar/webusers.htm .
For example, from a little web searching for the SPXL S&P 500 3X leveraged exchange traded fund, I see tjat Direxion's June 15, 2016 statutory prospects for at SPXL, TNA, ERX, TECL, TYD, TMF, LABU, SPXS, TZA, ERY, TECS, TYO, TMV and LABD, according to
http://direxioninvestments.onlinepr...-6-15-16-PRO/DailyETF-3X-Supp-6-15-16-PRO.pdf includes the following text on the fifth page of the PDF (the unnumbered page immediate before page before the table of contents):
The language about the gains also being limited makes me think that these particular funds might be selling very high calls in order to buy very low puts to pay for some downside protection. If they are, my guess is that these would be entirely or mostly off-exchange trades made with the opposite Direxion fund covering approximately the lower of the net asset values of the two funds (for examples, SPXL with SPXS).
Edit: Clarifying that last sentence, I mean that there is probably some standing contract between the various Direxion funds to do this automatically, not that staff at Direxion negotiate and sign such contracts between their funds each day, but it's complete guesswork on my part.