I want to retrieve only sheet's data from a spreadsheet with formatting.
How to achieve the same with Sheets Api?
It isn't clear from your question just what kind of data you want to get. Do you want to retrieve the values as they're formatted in the Google Sheets UI? If so, then use the spreadsheets.values.get API. The parameter valueRenderOption controls how the values are formatted. By default, the value is FORMATTED_VALUE, which will return the data as it's formatted in the Sheets UI. Other values are listed on the ValueRenderOption reference page. See the Basic Reading sample for more information.
If you want to retrieve the information about the format itself, use the spreadsheets.get API. Format information is in the response's CellData (at sheets.data.rowData.values), in both the userEnteredFormat and effectiveFormat fields.