Where do the 2 electrons and H⁺ go when NADPH is turned into NADP⁺ during the Calvin Cycle?
A reasonable source of information about the Calvin Cycle is Berg et al., but for this reaction the full structures are not shown. I therefore show them below in a diagram of my own:



I have coloured the hydrogen atoms to show where they go in reducing the phosphoglycerate (acid) to an aldehyde. You can think of the two electrons being used to form the additional covalent bond.

(The hydrogen phosphate is actually in equilibrium with other phosphate species, but this is not relevant to your question and so is not shown.)