@Mynock74vampiric touch and a dagger in the other hand. Can player attack with both using dagger as a bonus action, or just the one act Vampiric touch isn't a weapon, so you can't use it with Two-Weapon Fighting, if that's what you mean.
— Rodney Thompson (@wotc_rodney) September 25, 2014
I think this is a RAW vs. RAI question and is really up to your DM in terms of what you’re trying to do.
By RAW, using your action to cast a spell, you are not able to make an “attack action” as well, so you would not be able to use a bonus action to attack with a second weapon as you never previously attacked with a weapon to begin with.
By RAI, it’s pretty much the same thing as I do not believe the D&D 5.0 staff meant for you to be able to make any kind of attack while casting a spell (which is why they went to such great lengths to break up the list of actions.)
However, that being said, if you were to fancy yourself as a two weapon fighter, who knew magic, I do not believe it would be beyond your ability to use a touch attack with one hand, and use your only bonus action to make an attack with your off hand. Especially since a touch attack/unarmed strike could very well be considered a light weapon for the purpose of two weapon fighting.
Thank you for your advice Noble ninja
(Casts Necrothread) There’s no RAI (Rules as Intended) provided by the SA/Crawford (currently or as of May 2015) that would allow for it, nor is there any credible RAI (Rules as Interpreted, which isn’t a discussion point in 5E) relative to the wording of the two weapon attack option and use of a maintained touch-spell feature.