How do I synthesise this tertiary amide from these 5 compounds?
You seem to have got the uses of the compounds right, but could not bring that knowledge together to apply it here. As you said, you first use the Grignard to add a methyl group to D

Let's call this compound K. Then, we use $\ce{NaCN}$ to convert the alcohol into a nitrile, then to a carboxylic acid rather than an amide, as this would be easier to work with for us.

Let's call this compound L. Now we are ready to start creating the actual compound. Nitrate C and then reduce it to create the amine and reduce the ketone.

Then add L to the product, followed by K. This order is followed as adding the alcohol before the acid may create a tertiary amine rather than the amide we need.