Coupling of silyl imine and aldehyde LDA is a strong base and probably deprotonates somewhere which I'm not sure about. It I would to make a guess it would probably be beta to the imine. This is following by nucleophilic attack of the carboanion onto the use of the second reagent Pr-CHO to generate an alcohol. But I'm not sure the purpose of the 3rd reagent (oxalic acid).
This is a Peterson olefination, specifically this one is from the synthesis of Roseophilin published in J. Am. Chem. Soc. (2001) 123 8509. The LDA deprotonates next to the silicon as both it and the adjacent imine stabilise the anion.

The Wikipedia page gives a good summary of the mechanism and why an acidic work up is used in this case to give the required double bond geometry (Wikipedia).


  


(Image from www.chem.wisc.edu)