If thou know not - This appears to be the reply of the virgins.
They know not exactly; and therefore direct the bride to the shepherds, who would give information.
Matthew Henry
Concise Bible Commentary
Observe the title given to Christ, O Thou whom my soul loveth. Those that do so, may come to him boldly, and may humbly plead with him. Is it with God's people a noon-time of outward troubles, inward conflicts? Christ has rest for them. Those whose souls love Jesus Christ, earnestly desire to share in the privileges of his flock. Turning aside from Christ is what gracious souls dread more than anything else. God is ready to answer prayer. Follow the track, ask for the good old way, observe the footsteps of the flock, look what has been the practice of godly people. Sit under the direction of good ministers; beside the tents of the under shepherds. Bring thy charge with thee, they shall all be welcome. It will be the earnest desire and prayer of the Christian, that God would so direct him in his worldly business, and so order his situation and employment, that he may have his Lord and Saviour always before him.
SDA Bible Commentary (limited)
Volume 1-7
8. If thou know not. Another voice is introduced. It may be that of Solomon, or it may be the playful response of the court ladies telling the Shulamite to be patient. In due time her lover will appear. In the meantime she is to continue watching her flocks.