How many letters does the top answer for “mark with small spots” have?

The most common answer is speckle (7 letters).

Crossword clue: mark with small spots

1 answer found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

speckle 7 letters wn-def

a small contrasting part of something

to mark with spots, or as with spots. 67% similar → bespot

a very small spot 50% similar → pinpoint, speck

variegate with spots or marks 50% similar → harlequin