What is the product of reaction between 3,3-dimethyl butanal and SeO2 followed by conc. OH- ions? So basically first step will be replacement of $\ce{-CH2 -}$ by a ($\ce{=O}$ bond) making a aldehyde and ketone side by side. Now what should I do after this? I tried attacking the aldehyde first as it is more electrophilic. I think both carbonyl groups will be attacked because of high concentration of hydroxyl ($\ce{OH-}$) ions. I even tried dehydration of  the formed product after attacking with $\ce{OH-}$ ions but I always end up with a ketone and a carboxylic acid by its side  after this.
In the first step, Riley Oxidation (selenium dioxide-mediated oxidation of methylene groups adjacent to carbonyls) is taking place. You will get A as:


A on reaction with conc. $\ce{OH-}$ (i.e. in strongly alkaline condition) undergoes redox reaction (famous Cannizzaro reaction). And terminal aldehyde will be oxidized to form the metal salt of acid, ketone will be reduced to form the alcohol, note that intramolecular reaction is taking place, to finally form the product B.