What "blobs" of molten material in Earth's interior are responsible for the rapidly moving north pole? Where are these blobs exactly?
The "blobs" referred to in the IFLS article are, more correctly, areas of strong magnetic flux at the Earth's surface. The term "blob" is not scientifically significant, it just refers to a region where the magnetic field coming from Earth's core is stronger than elsewhere. Often we'd depict the magnetic field with a contour map of field strength, giving peaks and troughs of strong and weak field the appearance of "blobs" or patches, like this summary image from the publication in question:


(source: P. Livermore, via ESA: http://www.esa.int/Applications/Observing_the_Earth/Swarm/Magnetic_north_and_the_elongating_blob)

The maps show the radial magnetic field strength at Earth's surface in 1999, and then the field in 2019, this time with a trail showing the movement of the North magnetic dip pole (the star) since 1999. The two "blobs" of stronger field can be seen to change, the one over Siberia gets bigger and pulls the pole towards it, away from the now smaller Canadian one.

These "blobs" of strong field on the maps aren't "molten material in Earth's interior", but we can infer from maps like this what the field would look like at the surface of the outer core, and then from there what the movement of the material within the outer core might have been in order to generate the magnetic field we've observed. This is thanks to (math heavy :( ) frozen-flux theorem, that essentially says magnetic field is "frozen" into the iron-rich fluid at the surface of the Earth's outer core, so acts like a tracer for the fluid movement at the top of the outer core.

For an idea of what the flow (labelled "|U|") of material at the surface of the core might look like during the last 20 years to produce the field (labelled "Br", note the flipped color scheme), here are stills from the same model cited by the publication's authors of the field and flow at the core surface in 1999 and 2017. The Canadian "blob" gets stretched out and weaker relative to a strengthening Siberian "blob", as the flow speeds up under Canada:


(Source: https://geodyn.univ-grenoble-alpes.fr/, play with the great visualisations, but the animations are enormous files!)

So yes, you can map the distinct location of these "blobs" of strong field (though only outside the core), but bear in mind the maps are plotted with largely irrelevant choices of contour levels -- the field is continuous and varies smoothly, it's been drawn like this to highlight the "blobs" more clearly.

(Edit: added images of field and flow at the core surface to clarify, and make this answer a bit long...)