I think a lot of people do not understand what a tax return says when they are asking to see his. Do you list your home on your tax return, do you list stock you own, do you list your cars? You will not see his assets. You should look at the financial documents he had to file to run for president to get the info you want.
I assume his tax return is large enough that it is audited every year. Thus I do not think you will find out that he did anything outside of the law from looking at the tax returns.
I think it is easy to identify most of his assets since they have his name on them.