How to dissolve composite In2O3 with SnO2 without affecting stainless steel?
In case your question is about the recovery of indium from ITO, the following might be helpful: 

In Recovery of indium from indium tin oxide by solvent extraction, published in Hydrometallurgy, 2011, 107, 56-61 (DOI), the abstract seems to suggest that $\ce{H2SO4}$ is more suitable than $\ce{HNO3}$. Furthermore, a solvent extraction scheme for indium, using di-(2-ethylhexyl)phosphoric acid (DEHPA) is proposed.

In Recovery of indium from used indium–tin oxide (ITO) targets, published in Hydrometallurgy, 2011, 105, 207-212 (DOI), the authors agree on using $\ce{H2SO4}$ (at 90 °C) and decrease the ymount of tin in solution by sulfide precipitation.