Is it obligatory for one who has unintentionally stepped on blood to remember Allah Almighty, and is it true that jinn are present over that blood?

There is no evidence for the desirability of remembering Allah when stepping on blood, nor is there any validity to the claim that a jinn would be above it. This is from matters of the unseen, which can only be established by a text. The remembrance of Allah is good in all circumstances, but its specification to this particular situation has not been reported in any text.