Oxidation numbers of atoms in Ti(SeO3)2?
The selenite anion ($\ce{SeO3^{2-}}$) has a net charge of -2. Titanium's oxidation state should be obvious given this information. As for selenium's oxidation state, since we know each oxygen has a charge of -2, and since the entire polyatomic anion has a net charge of -2, the following equation must balance:

$$\ce{Se}+3 \cdot (-2)=-2$$