Substrate level phosphorylation occurs --------------------.

Substrate level phosphorylation is the direct synthesis of ATP from ADP by the transfer of a phosphate group from a phosphorylated reactive intermediate.

During glycolysis, which takes place in the cytoplasm, substrate level phosphorylation occurs at two steps: the conversion of $1,3$-bisphosphoglycerate to $3$-phosphoglyceric acid and the conversion of phosphoenolpyruvate to pyruvic acid.

During the Krebs cycle, which takes place in the mitochondrial matrix, substrate level phosphorylation occurs during the conversion of succinyl-CoA to succinic acid, where a molecule of GTP (which is then used to form ATP) is synthesized.

Therefore, substrate level phosphorylation occurs in both the cytoplasm of the cells and the matrix of mitochondria.

Answer: in cytoplasm of the cells and matrix of mitochondria.