Identifying an element in Selendroid is same as in Selenium.
Sample code from the official website,
SelendroidCapabilities capa = new SelendroidCapabilities("io.selendroid.testapp:0.17.0");
WebDriver driver = new SelendroidDriver(capa);
WebElement inputField = driver.findElement(By.id("my_text_field"));
Assert.assertEquals("true", inputField.getAttribute("enabled"));
inputField.sendKeys("Selendroid");
Assert.assertEquals("Selendroid", inputField.getText());
driver.quit();
Apart from id, you can use className, linkedText, partialLinkedText, name, tagName, xpath, cssSelector like in Selenium.