I am familiar with the fact that Magnetars have a really strong magnetic field and an ordinary star such as the Sun has a very strong gravitational field. But what about the opposite? What is the strength of the gravitational field of a Magnetar and how strong is the magnetic field of an ordinary star?
The surface gravitational field of a magnetar is much much stronger than that of an ordinary star. magnetars are types of neutron stars, which are compact objects for which general relativity is inherently necessary, while ordinary stars can be described classically, for the most part. The sun certainly has a magnetic field (note that solar prominences are basically jets of plasma that trace magnetic field lines of the sun), but the fields involved are no where close to those of a neutron star, which will have its magnetic field enhanced during the collapse process.