I found this dua in duas.org but I am wondering about the instruction to write on a piece of sugar this verse.
Proven Supplication for increasing memory ( Tohfatul Hashmiya)

Write on seven pieces of sugar and eat a piece everyday. Write on the first one:

فَتَعٰلَی اللهُ الْمَلِكُ الْحَقُّ.

Fataa’a’lallaahul malikul haqq

Supremely exalted is therefore Allah, the King, the Truth,[1]
I dont understand what is meant by sugar, is it the small sugar cube or any type of sugar.

by

Yes sugar cubes means any ordinary sugar cubes found in the market.