Thank you for contacting us and for your question.
Parsing the filter expression is the difficult way to achieving this scenario. I'd suggest that you iterate through all the columns of the grid and inspect their CurrentValue and CurrentFilterFunction properties. From those you can get both the filter value and the filter operator and of course you have the column's DataField that gives you the title of the SPField to which it is bound. Having this information, you can employ it to construct your CAML queries.
If further questions arise, do let us know.
All the best,
the Telerik team
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