If you highlighted the 4 strings of the Ukulele (default tuning) to notes on the piano, where would they come in relation to middle C?
The standard tuning of a Ukulele is a bit confusing because it is not strictly ascending.
This tuning is g4-c4-e4-a4, it means that the corresponding notes are G above middle C, middle C, E above middle C, A above middle C, from the string which is highest on the fretboard to the string which is closest to the ground.
It is easy to play it on the piano with the right hand and the fingering 1-2-4-5.
If you mount a thicker string for the G you can use the variant g3-c4-e4-a4 (the G one octave below) which is closer to the kind of tuning you have on a guitar (successive fourths). In this case the first string is G below middle C. It is more difficult to play the resulting piano chord with one hand.
Note that using different tunings on a ukulele for a given song is very frequent. On sheet-music there is usually a little diagram for the tuning in the form of a tablature.