struct accounts
{
  eosio::asset balance;
  uint64_t primary_key() const {return balance.symbol.code().raw();}
};
eosio::multi_index< eosio::name("accounts"), accounts > accounts_table;

accounts_table tmp(eosio::name("TOKEN_CONTRACT"), eosio::name("ACCOUNT_NAME"));
eosio::symbol TOKEN_SYMBOL = whatever the token symbol is;
auto itr = tmp.find(TOKEN_SYMBOL.code().raw());
eosio::check(itr != tmp.end(), "The token doesn't exist in the token contract, or the account doesn't own any of these tokens");
auto balance = itr->balance;
eosio::print("My balance is ",balance);