I’m learning music theory and I found a music sheet that I attach one part in a picture. If you see in the Treble Cleff, there are 8 eighth dotted notes and is a 4/4 signature. Like is a 4/4 is not supposed to be only the eighth notes alone without be dotted? Or why are dotted? It’s supposed 2 eighth notes make 1 quarter note and 4 quarter notes fill the 4/4 signature no? But why are dotted, is not required the dot no?
The notes in the treble clef are not dotted eighth notes, but just plain eighth notes. The dots beneath the note heads are articulation marks which mean that the notes should be played staccato. If the stems were down instead of up the dots would be probably be above the note heads in your example, but articulation marks may in general be placed either above or below the note with the goal of maximizing legibility.
In addition to David's as-usual great answer, I thought I'd offer a clarification to a common misunderstanding among beginning musicians:
Staccato does not mean short. The term comes from the Italian for "detached," thus staccato actually just means separated. Just how separated is up for interpretation, but in my experience beginning musicians often play staccato pitches too short. Typically this is because they are conceptualizing them as to be played "short" instead of "separated."