What country (sovereign) lies entirely within (inside) another country,
It is not an Enclave?
Two possible solutions
In a word it could be
Oman which is written inside Romania, but is not a geographical enclave.
Following on from Tom's answer, the second one is
Mali which is in Somalia
Monaco, which on land is bordered by France from all sides and whose maritime borders are completely surrounded by French territorial waters. It doesn't count as an enclave because it's on the coast.
It could be
since that lies entirely within
(inside) another country
I presume there's others by that logic
Could it be
This is because
It’s a city state surrounded by Indonesia, but it’s not an enclave?
Based on existing answers, it's:
Russia, which is inside Belorussia
or, if you prefer
in Belorussian, Русь inside Беларусь (using slightly glorious, less standard country name).
Alternately and more geographically,
Munich in Italian is Monaco, and it lies completely within Germany, but Monaco is also a sovereign country. And it's not an enclave, it's a homonym.
romania - oman
somalia - mali
Somekind of inside
dominican republic - dominica
equatorial guinea - guinea
guinea-bissau - guinea
nigeria - niger
papua new guinea - guinea
south sudan - sudan
It can be vatican city. As it is completely surrounded by rome which is in Italy