I would like to create some kind of drink to dissolve my multivitamin in but I don’t what it would dissolve best in.
You’re going to need a suspension - unless you plan on drinking some sort of acid mixture. fat soluble vitamins float in water, and water soluble vitamins just sit there in oils. It boils down to oil and water not mixing.
You could go with ultrasonic emulsification like we tried with clear soylent. Dissolve your fat solubles in oil, then emulsify it in a solution of your water solubles with an ultrasonic device (a ~$20 jewelery cleaner works nicely.)