Which substance is more solubility in ether and benzene? glyoxal or oxalic acid?

Glyoxal will be more soluble that oxalic acid. Carboxylic acids tend to be very insoluble in nonpolar solvents like ether and benzene. Glyoxal, even though it is a polar molecule, it's polarity will be small enough so that the dipoles will almost cancel each other out enough the make it weakly polar at best.