Assalamu'alaykum warahmatullahi wabarokatuh. Shaikh. I want to ask. What is ruling on black thing that look like a house lizard droppings/dung (فضلات الوزغ) if one take the opinion that house lizard have flowing blood (له نفس سائل) so his droppings is najis in that opinion?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

We are not aware of the reality of this thing; therefore, we cannot issue a Fatwa on the purity or impurity of its excrements.
Assuming that it has flowing blood, then its excrement is impure.

An-Natf fi al-Fatawa authored by Abul-Hasan as-Sughdi, from the Hanafi School of jurisprudence, reads:

“Whatever has liquid blood, such as a mouse, a snake, a gecko and a hedgehog, its urine is impure.” [End of quote]

Allah knows best.